Intra- and interannual variability in the larval fish assemblage off Gran Canaria (Canary Islands) over 2005–2007

The present study provides the longest and most intensive plankton and larval fish seasonal variability analysis in the Canary Islands and forms a basis for understanding life cycle scheduling and interactions among species, as well as the potential variability in transport processes of early life stages. Larval fish assemblages were studied weekly at Gran Canaria Island, Canary Islands, from January 2005 to June 2007, which represented two contrasting hydrological and biological periods. The former year was characterized by lower temperature and salinity that increased through 2006 and 2007. In contrast, chlorophyll concentration and mesozooplankton biomass decreased through the same period, especially when only the late winter bloom period was evaluated. However, ichthyoplankton abundance did not exhibit any clear pattern, as larger values were observed during 2006. The larval fish community of this oceanic island, located near the NW African upwelling, was composed of both neritic and oceanic taxa. Two families accounted for almost half of the collected larvae: Clupeidae (21.9%) and Myctophidae (20.5%). Although total larval concentration did not exhibit any seasonal peak linked to changes in zooplankton, the ichthyoplankton composition gradually changed during the year due to the high diversity and extended spawning periods of the fish species represented in samples. “Winter” and “summer” larval assemblages were identified, corresponding to the mixing and stratification periods of the water column, respectively. These assemblages were characterized by changes in the contribution of the most abundant annual taxa (Sardinella aurita, Cyclothone braueri, Ceratoscopelus spp. and Gobids) and by the presence of larvae of winter (Pagellus bogaraveo, Pomacentridae sp1) or summer spawners (Pomacentridae sp2, Trachinus draco, Arnoglossus thori, Tetraodontidae sp1). Upwelling filaments shed from the NW African coast reached the sampling area three times during this study, but changes in the local larval community were only detected in August 2005.     

Larval fish assemblages in Independencia Bay,Pisco, Peru: temporal and spatial relationships

The structure of the larval fish assemblages in Independencia Bay on the coast of Peru was examined using a combination of univariate and multivariate techniques. The plankton of Independencia Bay was sampled during 2000, to ascertain ichthyoplankton composition, abundance, and seasonality. These data were used to assess the function of the bay as spawning and nursery grounds and were related to the regional oceanography. In total, 16,156 fish larvae, representing 34 families, 48 genera, and 48 species were collected. Engraulidae, Normanichthyidae, Blenniidae, Gobiesocidae, Haemulidae, Labrisomidae, Pinguipedidae, and Atherinidae comprised 96.8% of the larvae captured; the remaining 3.2% included 26 families. Greatest mean larval fish densities, 319–1,381 per 100 m³, were recorded between September and November, suggesting a major spring spawning period. The most abundant fish larvae during this period were preflexion stage mote sculpins (Normanichthyidae) and newly hatched and preflexion stage anchovies (Engraulidae). A second, smaller summer peak was dominated by preflexion stage anchovies, followed by preflexion stage mote sculpins. The occurrence of high larval fish densities and the wide range of larval stages suggest that Independencia Bay is a regionally important spawning and nursery ground for marine fish. The principal component analysis showed that temperature and salinity were the dominant variables within the first two principal components, which accounted for 74.4% of the variation in environmental conditions. These conditions varied over time, station, and depth; however, interaction terms could not clearly be identified. Fitting a multinomial logistic model showed that larval fish assemblages and environmental conditions were associated in a complex way. The spring and summer ichthyoplankton abundance peaks in Independencia Bay coincided with high zooplankton standing stock and also coincided approximately with the periods of increased upwelling in the area.Communicated by O. Kinne, Oldendorf/Luhe     

Vertical structure of very nearshore larval fish assemblages in a temperate rocky coast

Small-scale vertical patterns of larval distribution were studied at a very nearshore larval fish assemblage, during the spring–summer period of several years, at two depth strata (surface and bottom) using sub-surface and bottom trawls. A total of 4,589 larvae (2,016 from surface samples and 2,573 from bottom samples) belonging to 62 taxa included in 22 families were collected. Most larvae belonged to coastal species. Although inter-annual variations in larval density and diversity could be found, total larval abundance was always higher near the bottom whereas diversity was higher at the surface. A marked distinction between the structure of surface and bottom assemblages was found. Sixteen taxa explained 95% of the similarity among surface samples. Larvae which contributed most to this similarity included species like clupeiformes, sparids and serranids, and also blenniids, tripterygiids and some labrids. In the bottom samples, fewer species were present, with only six taxa, almost exclusively from species which lay demersal eggs, contributing to 95% of the similarity between samples. Larvae present at the surface were significantly smaller than at the bottom. For some of the most abundant species found at the bottom, only small larvae occurred at the surface while the whole range of sizes was present at the bottom, indicating that larvae may be completing the entire pelagic phase near the adults’ habitat. These results indicate that larval retention near the reefs probably occurs for these species, although for others dispersal seems to be the prevailing mechanism.     

Spatio-temporal structure of pelagic larval and juvenile fish assemblages in coastal areas of New Caledonia,southwest Pacific

This study aims at describing the diversity and composition of larval and juvenile fish assemblages in coastal areas of New Caledonia, southwest Pacific, and identifying the environmental factors that influence the seasonal and spatial patterns of these assemblages. A total of 97 taxa belonging to 7 orders and 26 familis were captured in three bays near Nouméa by light trapping every month between January 2002 and June 2003. The assemblages were dominated by Clupeiform larvae and juveniles (96.4% of total abundance) and followed by Perciform larvae (3%). The number of taxa per sample varied from less than five in July–August to more than ten in October–November and abundances followed the same seasonal pattern. Analyses of similarity showed significant differences in the assemblages caught in the three bays and analyses of contribution to the dissimilarity revealed that these differences were due to the most abundant families. The constant part of the relationship between environmental variables and the composition of assemblages was assessed by the partial triadic analysis STATICO, a statistical approach that takes into account the strong seasonality of the data. Rainfall, wind direction and thermal stratification of the water column were found to play a major role in the structure of the assemblages, although tidal amplitude and wind speed became important when Clupeidae and Engraulididae were excluded from the analyses. The richness, relative abundances and seasonal variations of the assemblages caught in three bays under study are close to what has been observed elsewhere in the tropics. This study shows the efficiency of the STATICO analysis for identifying the environmental factors that have a permanent effect on assemblages and sorting them out from those which act temporally or on specific locations. The high abundances and diversity of coral-reef fish larvae observed in coastal zones of New Caledonia suggest that further studies are needed to fully explore the role of the coastal zones of New Caledonia as nurseries.     

Feeding opportunities of larval and juvenile cod (Gadus morhua) in a Greenlandic fjord: temporal and spatial linkages between cod and their preferred prey

Feeding of fish depends on a spatial and temporal match with prey, and since larval and juvenile feeding can be highly selective, their preferences for given prey sizes and taxa should be considered when quantifying the actual availability of potential prey. We investigated the diet and prey preferences of the early-life stages of Atlantic cod (Gadus morhua) to quantify the availability of prey during a spring-summer season in a West Greenlandic fjord. We hypothesized that abundances of larval and juvenile cod at size were synchronized to optimal availability of preferred prey in space and time. The present analysis is based on nine cruises each covering 5 stations visited between 24 May and 5 August 2010 comparing zooplankton abundance, cod gut content and distribution patterns. Cod 4–25 mm in length preferred prey of about 5 % of their own length. During ontogeny, their preferences changed from calanoid nauplii towards Pseudocalanus spp. and Calanus spp. copepodites. The larvae/juvenile had an exceptionally high dietary contribution from cladocerans, which were highly preferred by cod larger than 9 mm, while the abundant Metridia longa and the non-calanoid copepods contributed less. These findings stress the importance of focusing on abundance of preferred prey when assessing the actual prey availability to young fish. We found a spatio-temporal overlap between cod and their preferred prey, and observations suggest that advection of both zooplankton and cod contributed to this overlap. Hence, the larval feeding opportunities might be sensitive to climate-related changes affecting the circulation patterns in this fjord.     

Larval ecology of the great barracuda, <Emphasis Type="Italic">Sphyraena barracuda</Emphasis>, and other sphyraenids in the Straits of Florida

The great barracuda (Sphyraena barracuda) is a widespread, ecologically and socioeconomically important coastal fish, yet very little is known about its larvae. We examined spawning and larval ecology of Western Atlantic sphyraenids using monthly ichthyoplankton samples collected over 2 years along a transect spanning the east–west axis of the Straits of Florida (SOF). Samples were dominated by the great barracuda (92.8%) and sennets (Sphyraena borealis and Sphyraena picudilla; 6.6%). While larval sennets and S. barracuda displayed similar vertical distributions (majority in upper 25 m), horizontal and temporal patterns of abundance suggested a spatial and temporal species replacement between larval S. barracuda and sennets that tracks adult ecology. The diet of both taxa consisted largely of copepods, with inclusion of fish larvae at 8 mm SL, and in S. barracuda alone, a switch in the wet season to exclusive piscivory by 12 mm SL (18 days post-hatch). A lack of piscivory in S. barracuda larvae captured in the dry season corresponded to slower larval growth than in the wet season. Larval growth was also related to size-at-hatch and larval age such that larvae that were larger at hatch or larger (older) at capture grew faster at earlier ages, suggesting faster larval growth, and indirectly larger hatch size, conveys a survival advantage. Unlike larval growth, instantaneous mortality rate did not differ with season, and no lunar cyclic patterns in spawning output were identified. Our results provide insight into the pelagic phase of sphyraenids and highlight the importance of both diet and hatch size to the growth and survival of fish larvae in low latitude oceanic environments.     

Evaluating day–night changes in shallow Mediterranean rocky reef fish assemblages by visual census

Ecological information on coastal fish distribution patterns and habitat use can be greatly improved by nocturnal samplings and observations. To this purpose, the structure of a Mediterranean fish assemblage inhabiting the shallow rocky littoral of Linosa Island (Sicily Strait, Italy) was examined by using visual census to detect possible diel variations in species composition and abundance. Day–night fish distribution patterns were investigated by multivariate and univariate analyses. Overall, 42 fish taxa belonging to 19 families were recorded: 35 during the day and 24 during the night. Seventeen species were common to both diurnal and nocturnal assemblages. Within the diurnal assemblage, Chromis chromis was the most represented species (37.2%), followed by Thalassoma pavo (23.2%) and Sparisoma cretense (10.8%). Within the nocturnal assemblage, the most abundant taxon was Atherina spp. (33.9%), followed by Apogon imberbis (26.4%) and Boops boops (11.5%). Our results indicated wide variation in the abundance and species composition during the day and during the night. Multi Dimensional Scaling plot showed a clear-cut separation between the two assemblages and analysis of similarities found significant differences as well. SIMPER analysis revealed that ten species individually contributed by more than 2.5% to the dissimilarity between diurnal and nocturnal assemblages, T. pavo, C. chromis and S. cretense being the first three species in order of decreasing percentage. ANOVA performed on species richness and fish abundance detected significant differences between diurnal and nocturnal assemblages, the latter showing far lower average values for both variables.     

Importance of macroalgal fields as coral reef fish nursery habitat in north-west Australia

Macroalgal fields are a feature of the shallow tropical benthos, yet their importance for coral reef fish population dynamics remains poorly understood. The abundance of fish recruits was recorded using underwater visual census at six macroalgal and 11 coral reef sites in the Montebello and Barrow Islands. Surveys identified 6,935 individual recruit fish from 105 species, 54 genera and 20 families. Of these, 1,401 recruits from 48 species, 31 genera and 14 families were observed in macroalgal sites. Sixteen of the 105 recruit species (15.2 %) were observed exclusively at macroalgal sites. Forty-two (87.5 %) of these species have been observed as adults on adjacent coral reefs. Species composition of fish recruits differed significantly between the two habitats. Corallivore, small omnivore and zooplanktivore recruits had significantly higher numbers in the coral sites, while the results clearly demonstrate that juveniles, within the genera Lethrinus and Choerodon, as well as large algal croppers, are predominantly found at macroalgal (74–100 %) rather than coral-dominated sites. High-canopy macroalgae cover was positively correlated with abundance of these taxa, particularly Lethrinids (r ² = 0.40). This study is the first to highlight the important attributes of tropical macroalgal fields and suggests that they have a similar role to seagrass meadows as essential juvenile habitat, thus warranting greater attention in conservation planning and ecological studies.     

Larval mesopelagic fish assemblages in the Kuroshio–Oyashio transition region of the western North Pacific

We examined larval mesopelagic fish assemblages, their distribution, and seasonal occurrence patterns in the Kuroshio–Oyashio transition region of the western North Pacific where complex hydrographic structures are observed due to the confluence of the Kuroshio Extension and Oyashio current. Larvae of the dominant families Myctophidae, Gonostomatidae, Bathylagidae, Sternoptychidae, and Phosichthyidae were represented by 31 species or types belonging to 24 genera. Based on species composition analysis using the Morishita–Horn similarity index, five assemblages were recognized: Oyashio, Spring Transition, Summer Transition, Kuroshio, and Slope Water assemblages. The distribution patterns of these assemblages corresponded closely with hydrographic structures such as position of the Oyashio and Kuroshio Extension fronts, warm core rings and streamers. Spring Transition (April) and Summer Transition (July–October) assemblages were the most important larval assemblages in the transition region. Larval abundances were low during late autumn and winter. The Spring Transition and Summer Transition assemblages were composed of subtropical, transitional, subarctic, and slope-water species, suggesting the importance of the transition region as nursery grounds of mesopelagic fishes of various origins from subarctic to subtropical waters. Larval fish transport by the Kuroshio, Oyashio, and Tsugaru Warm currents into the transition region is discussed.     

Structure,composition and seasonal dynamics of the larval and juvenile fish community in the mangrove estuary of Tanshui River,Taiwan

The temporal and spatial patterns of species composition and abundance of fish larvae and juveniles in the Tanshui River mangrove estuary (Taiwan) were studied monthly using a drift bag-net in daylight. A total of 44591 individuals representing 55 families and 105 species were collected over 12 mo (August 1989 to July 1990). The community was dominated numerically by a few species. Sardinella melanura was most numerous, making up 70.15% of the total catch, followed by Stolephorus buccaneeri (19.59%), Thryssa kammalensis (2.96%), and Gerres abbreviatus (2.61%). These four species constituted ca. 95% of the total catch, the remaining 5% consisted of another 101 species. This estuary functions as a nursery and feeding area in the early life history of these fish. There was a separation in peak-immigration and seasonal utilization of the estuary by the dominant species. The abundance of fish larvae and juveniles decreased in an upstream direction.     

Diurnal and lunar patterns of larval recruitment of Brachyura into a mangrove estuary system in Ranong Province, Thailand

The present study followed the temporal recruitment pattern of brachyuran larvae in a mangrove tidal creek on the Andaman Sea coast of Ranong Province, Thailand, based on the assumption that the processes governing recruitment are important for the overall population dynamics of mangrove brachyuran crabs. Plankton net samples were taken on five occasions: on two new moon spring tides, one waxing moon neap tide, one full moon spring tide and one waning moon neap tide during October and November 1997. In addition collectors for larval crab megalopae were employed every 3 days through one dry season and one wet season (March–October 1998). Both the plankton net samples and collector samples revealed four major brachyuran groups in three families: Ocypodidae, Grapsidae and Portunidae. The grapsid group was further separated into two morphotypes which were identified as Metaplax and sesarmid species. Identified group mean numbers per cubic metre were ocypodids 3.0, sesarmids 0.8 and Metaplax 0.5, while portunid megalopae were very scarce (≪0.1 m⁻³). Further analysis of plankton net samples showed that when considering the parameters date, depth, current direction and the diel cycle, Metaplax and ocypodids distribute differently in the tidal and lunar cycle. Metaplax recruitment dominates on flood tides and on bottom layers, followed by middle and surface layers. Conversely, ocypodid abundance varied significantly with date only. Notably recruitment was not dependent on the diel cycle for either group. The collector samples of megalopae showed that recruitment of ocypodids, Metaplax and sesarmids occurred on full and new moon spring tides, while portunid megalopae preferred to settle on full moon spring tides. Since tidal currents were related to the lunar cycle megalopa groups are also cross-correlated with tidal amplitude, except for the portunid group. It is concluded that megalopae recruit in a similar manner to what has been found in other regions of the world, except that the abundance of ocypodids and Metaplax is not influenced by the diel cycle. Received: 14 February 2000 / Accepted: 24 November 2000     

Nematode assemblages from <Emphasis Type="Italic">Avicennia</Emphasis><Emphasis Type="Italic">marina</Emphasis> leaf litter in a temperate mangrove forest in south-eastern Australia

Meiofauna from Avicennia marina leaf litter in a temperate mangrove forest was enumerated, and the nematode assemblages compared on the bases of leaf colour (used as a guide to leaf age) and shore horizon where samples were collected. Twenty-one putative nematode species were collected from 48 leaf litter samples. Univariate analyses indicated that neither the colour of the leaf nor the shore horizon significantly affected abundance of nematodes. However, of the four (2Ƕ) treatment groups, rarefaction curves revealed highest diversity on brown leaves from under the shade of the tree canopy (H'=0.751ǂ.126 SE, n=17). Species diversity of leaf litter nematodes was lower in this temperate mangrove system than reported from tropical mangrove studies. ANOSIM tests confirmed a significant effect of shore horizon on nematode assemblages. The dominant feeding group among nematodes was non-selective deposit feeders (7/21 species, but 77% of all nematodes). Epigrowth grazers were represented by 8/21 species of nematodes, but only 19% of the total number. Excised leaves became skeletonised by about 15 weeks. Shorter temporal scales of life cycles of nematodes compared with leaf degradation, and the dynamic nature of epibiontic assemblages, probably explain the similar assemblage structure on yellow and brown leaves.     

Diel and tidal cycles regulate larval dynamics in salt marshes and mangrove forests

Variation in the release and recruitment of larvae of estuarine invertebrates affects the distribution and abundance of adults, as well as trophic interactions in both the plankton and the benthos. Larval release and supply are often timed to environmental cycles such as the diel and tidal cycles. Here, we determined using plankton tows whether the abundance of larvae spanning salt marsh and mangrove habitats across the intertidal landscape varied with diel and tidal cycles. Using three different sampling designs across two sites and within each of two estuaries over a 12-month period, we covered a range of spatial and temporal scales. This allowed us to test the general prediction that densities of meroplankton in the water column would be greater during nocturnal ebb tides than during other phases of the diel or tidal cycle. As predicted, nocturnal ebb tides yielded the highest densities of meroplanktonic larvae and were dominated by first-stage crab zoeae and this finding was most pronounced in the salt marsh. Throughout the course of the year, greater numbers of meroplankters consistently occurred during the ebb tide compared with the flood tide. The densities of other taxa (e.g. gastropods and polychaetes) showed no clear trends with diel or tidal cycles. This study highlights the effects of these pervasive physical cycles on the timing of larval release and supply in the salt marsh–mangrove complex, and emphasises their contribution to the trophic interactions and the dynamics of benthic populations within estuaries.     

Horizontal and vertical trends in the distributions of larval fishes in coastal waters off central New South Wales,Australia

Larval fishes were sampled across six transects perpendicular to a 50 km section of the coast off Sydney, Australia, in April/May and August/September 1990. Samples were collected at the surface and at depth (20 to 30 m) at three locations across each transect; over the 30, 70 and 100 m depth contours. There was a large level of heterogeneity in the horizontal and vertical distributions of most taxa examined, and no general pattern of distribution was evident for the whole assemblage. Classification analyses revealed that the major differences between assemblages were related to depth. Horizontal trends in the distributions of the abundant taxa were evident in the inshore-offshore direction, but not longshore. Seven taxa belonging to the families Gobiidae, Labridae, Sillaginidae, Sparidae, Ambassidae, Clupeidae and Clinidae/Tripterygiidae were most abundant inshore, whereas 4 taxa of the families Cepolidae, Percichthyidae, Cheilodactylidae and Gonorynchidae were generally more abundant offshore and 24 taxa showed no discrete horizontal trends across transects. More taxa and individuals were generally caught at depth than at the surface and this was evident across all transects. Twenty taxa were more numerous at depth, whereas 4 taxa, the Cheilodactylidae, Gonorynchidae, Mullidae and Scorpididae, were most abundant at the surface and 11 taxa showed no difference in densities between depths. Ontogenetic differences in the distributions of some larvae were evident. The mean size of larval Liza argentea (Mulgilidae) caught was greater offshore than inshore, and greater at the surface than at depth. In contrast, larger Pseudocaranx dentex (Carangidae) occurred in greater numbers at depth than at the surface. The data emphasise that the assemblages of larval fishes in coastal waters off central New South Wales cannot be modelled as a single unit, which concurs with the findings in other temperate and tropical vaters. Furthermore, the data denote the need to spatially stratify sampling in these waters in order to assess seasonal changes in these assemblages.     

The distribution of herbivorous fishes on the Great Barrier Reef

The composition and functionality of ecologically important herbivorous fish assemblages were examined throughout much of Australia’s Great Barrier Reef (GBR). Diversity and abundance of surgeonfishes (Acanthuridae), parrotfishes (Labridae) and rabbitfishes (Siganidae) were strongly associated with position on the continental shelf, whilst effects of latitude were weaker and inconsistent. Species distributions varied considerably amongst taxonomic groups; parrotfishes were mostly widespread whilst distributions of surgeonfishes were often restricted. Most inshore environments supported depauperate herbivore assemblages dominated by different taxa and functional groups compared with assemblages in offshore environments. There were also strong cross-shelf transitions in the main taxa performing each functional role. Overall, this study show that the functional contributions of herbivorous fish assemblages to important ecosystem processes and the contributing taxa vary considerably amongst different GBR environments. Additionally, the two most numerically dominant herbivores actively select detritus, not algae, supporting increasing evidence for the importance of detritus in coral reef ecology.     

Hydrography and distribution dynamics of larval and juvenile fishes in the coastal waters of the Tanshui River estuary,Taiwan, with reference to estuarine larval transport

Distribution dynamics of fish larvae and juveniles in the coastal waters of the Tanshui River, Taiwan was studied fortnightly using surface horizontal tows with a larval net in daytime during the period from early April through early June 1991. Environmental factors, including water temperature, salinity, dissolved oxygen, pH, transparency and depth at sampling stations, were also monitored. A total of 10737 fish eggs and 1387 individuals, representing 43 families and 93 species, was collected during five cruises from 12 stations in the coastal waters. Most fish were estuarine-dependent marine species. Liza macrolepis, Ambassis gymnocephalus, Terapon jarbua, Mullidae and Gobiidae were the most dominant, making up 64.7% of the total catch. Early life stages, including egg, preflexion, flexion and postflexion larvae were abundant in surface samples. However, yolk-sac larvae were absent in the surface water, probably due to an ontogenetic behavioral shift as a consequence of a change in specific weight during early development. The species composition of fish larvae and juveniles was related to the microhabitats found in the coastal waters. The physico-chemical conditions, along with ontogenetic behavior, played an important role in larval fish distribution in the coastal waters.     

Species composition,community structure and zoogeography of fishes of mangrove estuaries in the Solomon Islands

Mangrove estuaries in the Solomon Islands are well developed, but are small and isolated from each other by extensive fringing coral reef lagoons. A total of 136 species of fish were recorded from 13 estuaries (6 estuaries in Kolombangara, 3 in New Georgia, 3 in Rendova and 1 in the Florida Group); none contained more than 50 species. Sampling took place during five 3 wk expeditions from 1986 to 1988. The mean biomass of 11.60 g m^–2 is comparable with that of similar estuaries in northern Australia. Cluster-analysis revealed two patterns of fish species composition. The first group, in which Gobiidae were the most numerous taxon, inhabited soft, muddy-bottom estuaries. The second group, dominated by Pomacentridae, lived in hard-bottom, log-strewn estuaries. The role of the estuaries as nursery grounds for coral reef species was assessed and found to be insignificant, but they are used as feeding grounds by mobile piscivorous species. The species composition of Solomon Island estuaries was compared with that of other Indo-Pacific estuaries. No endemic species were found and the fauna is typical of such mangrove systems throughout the region. However, several taxa that are common in Australia or New Guinea were not found, notably Ariidae, Centropomidae,Pomadasys, and Sciaenidae. These absentees, and the fish fauna as a whole, are discussed in relation to the position of the Solomon Islands at the western edge of the Pacific Plate, the effects of deep-ocean trenches, the recent geological origin of the islands, and possible methods of colonisation from nearby mangroves in Australia and New Guinea. The importance of larval durations and dispersal to colonisation are discussed in relation to oceanic circulation patterns in the Solomon Sea.     

Horizontal distribution patterns of presettlement reef fish: are they influenced by the proximity of reefs?

The distribution patterns of presettlement reef fish and how they were influenced by the proximity of reefs were investigated off the coast of Northland, New Zealand, from 1981–1986. We used ichthyoplankton tows and visual counts of fish. Distributions of presettlement fish of some species were influenced by the proximity of reefs, regardless of whether reefs were on the coast of the mainland or islands across the shelf. Presettlement fish of families that lay demersal eggs were most abundant near reefs: Gobiescocidae, Acanthoclinidae, Tripterygiidae, Eleotridae, and Gobiidae. The distribution of presettlement sparids, mullids (pelagic eggs), and blenniids and monacanthids (demersal eggs) was not determined in a predictable way by the proximity of reefs. High-frequency sampling over three days suggested that patches of presettlement sparids of 1 to 2 km in dimension may move quickly through a study area. High abundance of presettlement gobiescocids and tripterygiids were found in 0 to 2 m of water over rocky reefs at high and low tides. Presettlement eleotrids were associated with reefs in deeper water (3 to 20 m) and in some habitats with aggregations of mysids. The lack of general patterns of distribution for presettlement reef fish suggests that modelling patterns of drift of these fish as a single group is inappropriate; this concurs with evidence from tropical waters.     

Spatiotemporal changes and fragmentation of mangroves and its effects on fish diversity in Ca Mau Province (Vietnam)

Mangroves are important economically and ecologically, however mangrove cover has declined dramatically leading to habitat fragmentation and biodiversity loss. Information on mangrove cover change, fragmentation and impacts on fish diversity is poorly understood. The aims of this study are to detect spatiotemporal changes and mangrove status, examine fragmentation changes and associated effects on fish diversity. Landsat images in1989, 2000, and 2013 were used to classify mangrove cover in Ca Mau Province (Vietnam) and validated against high resolution Pleiades imagery. Fragmentation changes in mangrove cover were examined using series of landscape metrics evaluated against fish diversity indices (Simpson’s index, Jaccard’s coefficient and relative abundance). Results show that mangrove cover has declined 24.6% in the province. Currently, high and moderately dense mangroves distribute in southern half of the region while the low density mangroves occurs in the northern half. Over the 24 year study periods, the number of patches and edge density has increased 58% and 53.9%, respectively, while the mean patch size and mean patch edge has decreased 52.3% and 26.6%. Fish diversity in the more highly fragmented mangrove area was 1.78 times lower than the less fragmented mangrove. The study illustrates the applicability of using Landsat satellite imagery for use in mangrove fragmentation studies as well as the impact of fragmentation.     

Effects of Artisanal Fishing on Caribbean Coral Reefs

Abstract:  Although the impacts of industrial fishing are widely recognized, marine ecosystems are generally considered less threatened by artisanal fisheries. To determine how coral reef fish assemblages and benthic communities are affected by artisanal fishing, we studied six Caribbean islands on which fishing pressure ranged from virtually none in Bonaire, increasing through Saba, Puerto Rico, St Lucia, and Dominica, and reaching very high intensities in Jamaica. Using stationary-point fish counts at 5 m and 15 m depth, we counted and estimated the lengths of all noncryptic, diurnal fish species within replicate 10-m-diameter areas. We estimated percent cover of coral and algae and determined reef structural complexity. From fish numbers and lengths we calculated mean fish biomass per count for the five most commercially important families. Groupers (Serranidae), snappers (Lutjanidae), parrotfish (Scaridae), and surgeonfish (Acanthuridae) showed order-of-magnitude differences in biomass among islands. Biomass fell as fishing pressure increased. Only grunts (Haemulidae) did not follow this pattern. Within families, larger-bodied species decreased as fishing intensified. Coral cover and structural complexity were highest on little-fished islands and lowest on those most fished. By contrast, algal cover was an order of magnitude higher in Jamaica than in Bonaire. These results suggest that following the Caribbean-wide mass mortality of herbivorous sea urchins in 1983–1984 and consequent declines in grazing pressure on reefs, herbivorous fishes have not controlled algae overgrowing corals in heavily fished areas but have restricted growth in lightly fished areas. In summary, differences among islands in the structure of fish and benthic assemblages suggest that intensive artisanal fishing has transformed Caribbean reefs.