Biogeographic patterns on shallow subtidal reefs in the western Indian Ocean

To resolve biogeographic limits and patterns on the east coast of Africa, the presence/absence and quantitative biomass data were collected from 55 shallow subtidal reefs along 4,800 km of coastline (5.2°–31.1°S). Multivariate analysis of distributions, trophic structure and biomass revealed two distinct marine provinces, the Tropical Indo-West Pacific and Subtropical Natal, with a transitional overlap (of ca. 120 km) located between Leven Point and Kosi Mouth on north-east South Africa. This region of overlap was one of three bioregions revealed by post hoc analyses. Biomass was unexpectedly highest in the tropics. ‘Auto-heterotrophs’ (species with autotrophic symbionts such as corals and clams), deposit feeders and grazers contributed significantly more biomass to the Tropical Indo-West Pacific Bioregion, whereas filter feeders dominated the Subtropical Natal Bioregion. ‘Auto-heterotrophs’ declined with latitude while filter feeders increased; soft corals made a defining contribution in the overlap bioregion. Possible underlying causes of these patterns include productivity, nutrient levels, riverine input, light penetration and temperature.     

Investigations on some tropical euphausiid species of the Indian Ocean

In spite of the great ecological importance of euphausiids in large areas of the sea, very little is known about their early developmental stages. During the 40th and 41st cruises of RV Vityaz (USSR) in the western part of the Indian Ocean, new information was obtained on the development of 2 species common in that area: Euphausia diomedeae and Slylocheiron carinatum. In E. diomedeae, the time between fertilization and hatching of the nauplius amounts to about 16 h; the metanauplius stage lasts 2 days, the calyptopis stage I also 2 days, and the calyptopis stage III up to 4 days, at water temperatures ranging from 22° to 26°C. The developmental stages of both species are described and illustrated.     

Biochemical composition of sedimentary organic matter in the coral reefs of Lakshadweep Archipelago,Indian Ocean

Surface sediments were collected from the shore and lagoons of Kavaratti, Kadamat Agatti and Pitti islands of Lakshadweep Archipelago during May 2015 and analysed for biochemical composition and quality of organic matter. The biochemical composition of sedimentary organic matter from the entire study area was characterised by the dominance of carbohydrates (CHO) followed by proteins (PRT) and finally lipids (LPD). PRT:CHO ratios were less than 1 and indicated the presence of aged organic matter in the islands. The poor nutritional quality of sediments to support benthic fauna was evident from the values of LPD:CHO ratios. The refractory nature of sediments and less availability of food to benthic source was supported by BPC:TOC ratios. Based on estimated ratios and biopolymeric carbon values, the trophic status of the study area was categorised as oligotrophic.     

Diversity and stability of herbivorous fishes on coral reefs

Biodiversity may provide insurance against ecosystem collapse by stabilizing assemblages that perform particular ecological functions (the "portfolio effect"). However, the extent to which this occurs in nature and the importance of different mechanisms that generate portfolio effects remain controversial. On coral reefs, herbivory helps maintain coral dominated states, so volatility in levels of herbivory has important implications for reef ecosystems. Here, we used an extensive time series of abundances on 35 reefs of the Great Barrier Reef of Australia to quantify the strength of the portfolio effect for herbivorous fishes. Then, we disentangled the contributions of two mechanisms that underlie it (compensatory interactions and differential responses to environmental fluctuations ["response diversity"]) by fitting a community-dynamic model that explicitly includes terms for both mechanisms. We found that portfolio effects operate strongly in herbivorous fishes, as shown by nearly independent fluctuations in abundances over time. Moreover, we found strong evidence for high response diversity, with nearly independent responses to environmental fluctuations. In contrast, we found little evidence that the portfolio effect in this system was enhanced by compensatory ecological interactions. Our results show that portfolio effects are driven principally by response diversity for herbivorous fishes on coral reefs. We conclude that portfolio effects can be very strong in nature and that, for coral reefs in particular, response diversity may help maintain herbivory above the threshold levels that trigger regime shifts.     

Sabaki River sediment load and coral stress: correlation between sediments and condition of the Malindi-Watamu reefs in Kenya (Indian Ocean)

Sediment discharges from rivers have a negative impact on coral reef ecosystems. Indicators of coral decline measured in the present study were: (1) injury to living stony corals; (2) soft coral cover; and (3) bare rocky substrate suitable for colonization by corals. The relationship between these indicators and the distribution of terrigenous sediment was studied for the Malindi-Watamu fringing reef complex along the Kenyan coast off East Africa during 1982 and 1983. Decline of this reef had been repeatedly noted during the preceding decade. The influence of terrigenous sediment from the Sabaki River appears to be strongest in the Watamu area in the south and in the northern-most part of the Malindi reef area. Correlations, between each of the above three coral stress response indicators, on the one hand, and quantitative indicators of sediment loading, on the other hand, were not clear. However, a combined coral stress indicator involving all three factors was shown to have a clear relationship with terrigenous sediment loading and provided a rapid means of field evaluation of the effects of sediment stress on stony corals. Values for the combined coral stress indicator were found to increase in proportion to increasing values of terrigenous sediment loads in both study areas. A higher coral stress indicator value means a high proportion of injured or algae infested corals, and/or a high soft coral cover, and/or a high proportion of rocky substrate suitable for, but unoccupied by, living corals.     

Effects of herbivory on zonation of Sargassum spp. within fringing reefs of the central Great Barrier Reef

A combination of small-scale transplants and herbivore exclusion was used to test the importance of herbivory, physiological tolerance limits, and recruitment and dispersal in regulating the distribution and abundance of the genus Sargassum on two nearshore fringing reefs of the central Great Barrier Reef, during 1992/1993. Sargassum (predominantly S. oligocystum and S. tenerrimum) were transplanted from reef-flat zones where they normally grow, to a seaward coral zone where they are not normally found. At Great Palm Island, coral-zone transplants only survived if protected from herbivores. At Brook Island, survival of uncaged coral-zone transplants was more variable but not significantly lower than plants returned to the Sargassum zone. Thus herbivory may be a major cause of the zonation patterns of adult Sargassum on these fringing reefs, but the importance of this factor varies between and within reefs. Since protected Sargassum survived and grew for up to 6 mo in the coral zone, the adult algae are not physiologically limited by any physical or chemical differences between zones. However, Sargassum recruitment to the coral zone was very low (mean 2.7 recruits m⁻² over 13 mo), and was not significantly affected by herbivores. Since rates of herbivory were relatively slow, effective exclusion of Sargassum from the coral zone by herbivores may depend on low recruitment of the algae. In a broader context, the distribution of Sargassum may depend on the combined spatial patterns of herbivory and recruitment. Received: 24 January 1997 / Accepted: 12 May 1997     

Diversity and community structure of symbiotic dinoflagellates from Caribbean coral reefs

A community ecology approach to the study of the most common group of zooxanthellae, dinoflagellates in the genus Symbiodinium, was applied to symbiotic invertebrate assemblages on coral reefs in the western Caribbean, off the Yucatan peninsula (Puerto Morelos, Mexico) and over 1000 km away in the northeastern Caribbean, at Lee Stocking Island, Bahamas. Sequence differences and intragenomic variation, as determined by denaturing gradient gel electrophoresis and sequencing of the internal transcribed spacer 2 (ITS 2) region, were used to classify these symbionts. Twenty-eight genetically distinct Symbiodinium types were identified, eleven of which were found in hosts from both Caribbean locations. A single symbiont population was detected in 72% of hosts from the Yucatan and 92% of hosts from the Bahamas. The reef-wide community distribution of these symbionts is dominated by a few types found in many different host taxa, while numerous rare types appear to have high specificity for a particular host species or genus. Clade or lineage A Symbiodinium spp. was restricted to compatible hosts located within 3-4 m of the surface, while Symbiodinium spp. types from other lineages displayed differences in vertical zonation correlated with ITS type but were independent of clade designation. A comparison of the symbiont types found in field-collected hosts with types previously cultured from these hosts indicates the existence of low density or "background"-symbiont populations and cryptic, potentially non-mutualistic types in some hosts.     

Taxonomic Uncertainty and the Loss of Biodiversity on Christmas Island,Indian Ocean

The taxonomic uniqueness of island populations is often uncertain which hinders effective prioritization for conservation. The Christmas Island shrew (Crocidura attenuata trichura) is the only member of the highly speciose eutherian family Soricidae recorded from Australia. It is currently classified as a subspecies of the Asian gray or long‐tailed shrew (C. attenuata), although it was originally described as a subspecies of the southeast Asian white‐toothed shrew (C. fuliginosa). The Christmas Island shrew is currently listed as endangered and has not been recorded in the wild since 1984–1985, when 2 specimens were collected after an 80‐year absence. We aimed to obtain DNA sequence data for cytochrome b (cytb) from Christmas Island shrew museum specimens to determine their taxonomic affinities and to confirm the identity of the 1980s specimens. The Cytb sequences from 5, 1898 specimens and a 1985 specimen were identical. In addition, the Christmas Island shrew cytb sequence was divergent at the species level from all available Crocidura cytb sequences. Rather than a population of a widespread species, current evidence suggests the Christmas Island shrew is a critically endangered endemic species, C. trichura, and a high priority for conservation. As the decisions typically required to save declining species can be delayed or deferred if the taxonomic status of the population in question is uncertain, it is hoped that the history of the Christmas Island shrew will encourage the clarification of taxonomy to be seen as an important first step in initiating informed and effective conservation action.     

Estimating the footprint of pollution on coral reefs with models of species turnover

Ecological communities typically change along gradients of human impact, although it is difficult to estimate the footprint of impacts for diffuse threats such as pollution. We developed a joint model (i.e., one that includes multiple species and their interactions with each other and environmental covariates) of benthic habitats on lagoonal coral reefs and used it to infer change in benthic composition along a gradient of distance from logging operations. The model estimated both changes in abundances of benthic groups and their compositional turnover, a type of beta diversity. We used the model to predict the footprint of turbidity impacts from past and recent logging. Benthic communities far from logging were dominated by branching corals, whereas communities close to logging had higher cover of dead coral, massive corals, and soft sediment. Recent impacts were predicted to be small relative to the extensive impacts of past logging because recent logging has occurred far from lagoonal reefs. Our model can be used more generally to estimate the footprint of human impacts on ecosystems and evaluate the benefits of conservation actions for ecosystems.     

Community interactions and zoogeography of the Indian Ocean Candaciidae (Copepoda: Calanoida)

Eighteen species of Candaciidae have been identified from collections made at 339 stations in the Indian Ocean. Most species are zonally distributed; however, on the eastern and western sides of the Indian Ocean, species ranges are extended north or south by boundary currents. Factor analysis was used to cluster phenotypically similar species based on 130 characters taken from the maxilla (a feeding appendage), the first swimming foot, and the fifth foot (a secondary sexual structure). Four morphological clusters were extracted. Clusterings based on separate factor analyses limited to characters from feeding or from sexually adapted appendages are in substantial agreement with the clusters based on composite morphology. Two geographically recurrent groups of species were also identified, one from equatorial waters, one from the central gyre. Each recurrent group is composed of species exceptionally different in body size and belonging to different morphological clusters. Niches of the species are compared using Hutchinson's multidimensional hypervolume as a model. An attempt is made to describe the niche of each species in terms of environmental variables measured at stations where the species was abundant. Environmental variables (dimensions) included in this study are space, time, temperature, food, oxygen and salinity. Mean niche adaptations of most of the species are separable from congeners along at least one niche dimension. It is proposed that community relationships among the Candaciidae developed to prevent both gamete loss and to avoid trophic competition. It is postulated that newly evolving species underwent contemporaneous displacement of both secondary sexual and trophic characters as a condition for sympatry, or diverged in their physiological adaptations to escape sympatric interference.Contribution No. 3686 of the Woods Hole Oceanographic Institution. This research was supported by NSF Grants GB 27405 and GA 43126 and is based on a doctoral dissertation submitted to the Curriculum in Marine Sciences of the University of North Carolina at Chapel Hill.     

Bioerosion of coral reefs by two Hawaiian parrotfishes: species, size differences and fishery implications

Parrotfishes can be significant bioeroders and sediment producers on coral reefs. We quantified the bioerosion rates of two similarly sized Hawaiian parrotfishes with two different feeding modes (Scarus rubroviolaceus—a scraper and Chlorurus perspicillatus—an excavator). The results showed that feeding modes did not affect bioerosion rates but that bioerosion rates were size dependent, with largest individuals (S. rubroviolaceus 45–54 cm FL) bioeroding up to 380 ± 67 kg ind⁻¹ year⁻¹. The size for onset of bioerosion capabilities for both species was 15 cm. Grazing by the two species consumed 60% of the carbonate production of the fore reef area, suggesting that large parrotfishes in Hawaii are ecologically important bioeroders. As individual large S. rubroviolaceus contributed disproportionately more to bioerosion and sediment production than the equivalent biomass of smaller conspecifics, management strategies designed to retain normal reef bioerosion rates should seek to preserve the historical size structure of S. rubroviolaceus populations and to especially protect the larger size classes.     

Larval biology of six species of the genus Conus (Gastropoda: Toxoglossa) in Hawaii,USA

Among the Hawaiian species in the genus Conus, larval life histories range from long-term planktotrophy to nonpelagic lecithotrophy. Prehatching developmental time, hatching size, pelagic period and total prejuvenile developmental time are all significantly correlated with egg size, while settling size is correlated with none of these larval characteristics. Therefore, larval life history patterns in the genus Conus appear to be determined by 2 sets of selective forces: the first influencing egg size, and the second stipulating settling size. As egg sizes become larger, hatching sizes and prehatching developmental time increase while pelagic periods and total prejuvenile developmental times decrease. Settling size appears to be related to water depth, but food requirements of newly metamorphosed juveniles may also be important.     

Production and fate of copepod fecal pellets across the Southern Indian Ocean

The vertical distribution of copepods, fecal pellets and the fecal pellet production of copepods were measured at seven stations across the Southern Indian Ocean from productive areas off South Africa to oligotrophic waters off Northern Australia during October/November 2006. We quantified export of copepod fecal pellet from surface waters and how much was retained. Furthermore, the potential impact of Oncaea spp. and harpacticoid copepods on fecal pellets degradation was evaluated and found to be regional substantial. The highest copepod abundance and fecal pellet production was found in the western nutrient-rich stations close to South Africa and the lowest at the central oligotrophic stations. The in situ copepod fecal pellet production varied between 1 and 1,000 μg C m⁻³ day⁻¹. At all stations, the retention of fecal pellets in the upper 400 m of the water column was more than 99% and the vertical export of fecal pellets was low (<0.02 mg m⁻² day⁻¹).     

West Indian Ocean phytoplankton: a numerical investigation of phytohydrographic regions and their characteristic phytoplankton associations

Phytoplankton samples were collected from a large area of the West Indian Ocean and 237 different species identified. The object of this study was to define structure in the species distributions and to relate this to environmental factors. Numerical methods of cluster analysis are described, with adaptation and application to this ecological study of phytoplankton. The phytoplankton stations were grouped according to their phytoplankton populations; these groupings were related firstly to the monsoon seasons, and secondly to the hydrology, in order to derive phytohydrographic regions. The species were then grouped according to hydrographical distribution in order to derive the floral elements (species associations) which typify the different regions. The samples divided seasonally into 2 overlapping clusters, those sampled prior to the South West Monsoon, and those sampled subsequently. In both seasonal groups 4 main phytohydrographic regions were isolated from (1) equatorial subsurface water; (2) the equatorial undercurrent boundary; (3) the South Equatorial Current; (4) the surface tropical water. A total of 11 different floral elements were derived to account for the phytohydrographic groupings. The distribution of the largest element (50 species) was centred in equatorial subsurface water. This element dominated all samples, and was considered to comprise the endemic Indian Ocean flora. The effects of the other minor floral elements were superimposed on the dominance or otherwise of this element in the samples. These different minor floral elements were characteristic of (a) different seasonal divisions; (b) regional differences in equatorial subsurface water; (c) traversing currents; (d) nutrientrich regions of instability.     

Diversity,abundance, and distribution of reef sharks on outer-shelf reefs of the Great Barrier Reef,Australia

Quantifying the distribution and habitat use of sharks is critical for understanding their ecological role and for establishing appropriate conservation and management regimes. On coral reefs, particularly the Great Barrier Reef (GBR), little is known regarding the distribution of sharks across major reef habitat types. In this study, we surveyed shark populations across outer-shelf reefs of the GBR in order to determine the diversity, abundance, and distribution of reef sharks across three major coral reef habitats: (1) the reef slope, (2) the back reef and (3) the reef flat. Model selection revealed that habitat was the principal factor influencing shark distribution and abundance. Specifically, overall shark abundance and diversity were significantly higher on the reef slope (and to a lesser degree, the back reef) than the reef flat. This confirms that shark populations are not homogeneously distributed across coral reefs. Thus, the results presented herein have important implications for shark population assessments. In addition, our results highlight the potential importance of the reef slope, with high levels of live coral cover and structural complexity, for sustaining reef shark populations. As this habitat is highly susceptible to disturbance events, this study provides a useful context for predicting and understanding how environmental degradation may influence reef shark populations in the future.     

Inter- and intraspecific patterns of reproductive effort in four species of cone shells (Conus spp.)

Patterns of reproductive effort were examined both within and between 4 species of the tropical marine gastropod genus Conus from Hawaii in 1979. Caloric content was measured for the somatic tissues of female cone shells and for their egg capsule masses. These data were used to calculate (1) current reproductive effort, which was the ratio of annual energy produced as spawn to the sum of the annual energy produced as spawn plus the annual energy produced as somatic tissue; and (2) weight-specific reproductive effort, which was the ratio of annual energy produced as spawn to the total energy content of the female body just before spawning. For C. pennaceus, during the approximately 10 yr of life of a female, current reproductive effort rose from about 0.35 at 2 yr to about 0.85 at 10 yr. In contrast, weight-specific reproductive effort remained relatively constant throughout life for C. pennaceus (about 0.2 to 0.5), C. abbreviatus (about 0.2 to 0.3), C. flavidus (about 0.2 to 0.3) and C. quercinus (about 0.1 to 0.2). It is suggested that weight-specific reproductive effort may be useful as an index of the selective importance of the survival cost of present reproduction, while current reproductive effort more closely reflects the selective importance of energy allocation tradeoffs. Data on the 4 species of Conus examined support the hypothesis that reproductive effort should be positively correlated with extrinsic adult mortality and negatively correlated with the variability of juvenile survivorship. The data also suggest a possible relationship between reproductive effort and the cost of parental care.     

Food resource utilization among five species of embiotocids at King Harbor,California, with preliminary estimates of caloric intake

The diets of 5 species of embiotocids (Rhacochilus vacca, Embiotoca jacksoni, Hypsurus caryi ryi, Phanerodon furcatus and Micrometrus minimus) from King Harbor, Redondo Beach, California, USA, are examined by means of a dietary survey, field feeding observations and bomb calorimetry of prey items. Each species is shown to have statistically different diets from all others, with the exception of H. caryi which apparently is a dietary intermediate between E. jacksoni and P. furcatus. Dietary overlap between E. jacksoni and H. caryi appears to have resulted in some competitive exclusion along other niche parameters. Estimated caloric intakes suggest that R. vacca has the highest caloric yield per bite and the lowest feeding rate of the species studied. Possible energetic advantages are found for diet specialization in R. vacca.     

Notes on the Nerita (Archaeogastropoda) populations of Aldabra Atoll,Indian Ocean

Nerita undata, N. plicata, N. polita, N. albicilla and N. textilis are common intertidal gastropods on Aldabra Atoll. Each species prefers a different level on the shore and/or different degrees of exposure to wave action. Patterns of zonation, population size-frequency structure and biomass are given. N. undata exhibits 2 distinct ecophenotypes. Normal types occur on expsed to moderately sheltered shores but are replaced by type B in extremely sheltered conditions. Differences in shell morphology and population structure are also noted. Foraging by all species was confined to hours of darkness, generally at low tide. Activity of N. polita was induced slightly on overcast days. N. undata and N. textilis are cryptically coloured and often visible during the day. N. plicata is conspicuous, but is protected by a strong shell. N. polita and N. albicilla are often brightly and variably coloured, but both are concealed during daylight. No Nerita were found infected with trematodes, suggesting that the degree of infection was extremely low. Habitats of the Aldabran Nerita are compared with 3 species on Barbados, West Indies.     

Genetic structure of Patagonian toothfish (Dissostichus eleginoides) populations on the Patagonian Shelf and Atlantic and western Indian Ocean Sectors of the Southern Ocean

The genetic structure of Patagonian toothfish populations in the Atlantic and western Indian Ocean Sectors of the Southern Ocean (SO) were analysed using partial sequences of the mitochondrial 12S rRNA gene and seven microsatellite loci. Both haplotype frequency data (F _ST>0.906, P<0.01) and microsatellite genotype frequency data (F _ST=0.0141–0.0338, P<0.05) indicated that populations of toothfish from around the Falkland Islands were genetically distinct from those at South Georgia (eastern Atlantic Sector SO), around Bouvet Island (western Atlantic Sector SO) and the Ob Seamount (western Indian Ocean Sector of the SO). Genetic differentiation between these populations is thought to result from hydrographic isolation, as the sites are separated by two, full-depth, ocean-fronts and topographic isolation, as samples are separated by deep water. The South Georgia, Bouvet and Ob Seamount samples were characterised by an identical haplotype. However, microsatellite genotype frequencies showed genetic differentiation between South Georgia samples and those obtained from around Bouvet Island and nearby seamounts (F _ST=0.0037, P<0.05). These areas are separated by large geographic distance and water in excess of 3,000 m deep, below the distributional range of toothfish (<2,200 m). No significant genetic differentiation was detected between samples around Bouvet Island and the Ob Seamount although comparisons may have been influenced by low sample size. These localities are linked by topographic features, including both ridges and seamounts, that may act as oceanic “stepping stones” for migration between these populations. As for other species of deep-sea fish, Patagonian toothfish populations are genetically structured at the regional and sub-regional scales.