Distribution and abundance patterns of two parapagurid hermit crabs (Crustacea: Decapoda: Anomura) along the west and south coasts of South Africa

A series of over 6 000 research-trawl samples collected along the west and south coasts of South Africa between 1987 and 2014 were analysed for the presence and biomass of two parapagurid hermit crabs, Sympagurus dimorphus and Parapagurus bouvieri. The percentage of trawls that landed S. dimorphus and P. bouvieri and the mean caught biomass were higher on the west than on the south coast for both the more-abundant S. dimorphus (30.59 vs 5.81% success and 287.88 vs 31.37 kg km^–2, respectively) and for the less-abundant P. bouvieri (13.76 vs 3.58% success and 38.56 vs 16.32 kg km^–2, respectively). Very few parapagurids were caught shallower than 150 m; thereafter, the proportion of trawls containing hermit crabs increased, peaking over the depth range 201–250 m for S. dimorphus (54%) and 401–450 m for P. bouvieri (51%), and declining steadily thereafter. On the west coast, the relative caught biomass of S. dimorphus increased significantly from north to south, but there was no apparent latitudinal trend in relative biomass for P. bouvieri. Similarly, there was a significant decline in caught biomass of S. dimorphus with increasing longitude along the south coast, but no apparent trend for P. bouvieri. Although this represents by far the most comprehensive global analyses of distribution and abundance patterns for parapagurids to date, extremely little remains known about the biology and ecological relationships of these species, or indeed of other members of the group.     

Lignin geochemistry of sediments from the Narragansett Bay Estuary

Cupric oxide oxidation has been employed to characterize the lignin geochemistry of Narragansett Bay sediments. Lignin concentrations throughout the estuary are low when expressed on a carbon-normalized basis, but can be characterized as enriched when expressed on a mass-normalized basis. This implies substantial dilution of the sedimentary lignin by inputs of lignin-poor carbon. Lignin concentrations do not correlate with the ¹³C isotopic composition of the sedimentary organic matter. These results are consistent with a sediment lignin component consisting of varying amounts of vascular plant debris and lignin-depleted organic matter, the latter originating from both marine (planktonic) and terrestrial (uncharacterized) sources. Compositional plots of lignin-derived phenols show that sediments in the upper estuary are influenced to a greater extent by gymnosperm lignin sources than those in the mid-and lower estuary. Given the extent to which the upper estuary is affected by pollution sources, inputs from anthropogenic discharges are the most likely cause of these compositional differences. However, an evaluation of processed paper products as an “anthropogenic” lignin source indicates that the lignin content of these materials is insufficient to account for the levels found in the sediments. Subsurface lignin compositions at an upper estuary site reveal that lignin originating from the inferred anthropogenic sources disappears at a depth shallower than that which would be expected based on the distribution of other trace organic pollutants (hydrocarbons and several synthetic organic compounds). We speculate that differences in either the depositional history or the degree of preservation of these two compound classes are responsible for the observed trends.     

Do predatory fish of benthic crustaceans vary between kelp and barren reef habitats in northeastern New Zealand?

Fish assemblages that included known predators of benthic crustaceans were compared between kelp and barren habitats in northeastern New Zealand using baited underwater video census methods. The benthic-feeding fish were observed in winter, spring/summer and autumn, as well as during night-time in spring/summer. Overall, the fish assemblages varied between barren and kelp habitat, being most marked in winter. Individual benthic-feeding species, such as grey mao mao (Scorpis lineolatus) and leatherjacket (Meuschenia scaber) were associated with barren habitat, while the spotted wrasse (Notolabrus celidotus) was more strongly associated with kelp habitat. The results suggest that changes in habitats on coastal reefs affect populations of species that are benthic predators, which may in turn influence the distribution and abundance of their prey species, such as juvenile spiny lobsters.     

A molecular and carbon isotopic study towards the origin and diagenetic fate of diaromatic carotenoids

Pyrolysates of high-molecular-weight sedimentary fractions of the Duvernay Formation (Western Canada Basin) are dominated by 1,2,3,4- and 1,2,3,5-tetramethylbenzene, which, generated via beta-cleavage, indicate the presence of diaromatic carotenoids in the macromolecular aggregates. This was substantiated by desulphurization of sulphur-rich aggregates of the polar fraction, which released (partly) hydrogenated carotenoids. Furthermore, these components were important constituents of the aromatic hydrocarbon fractions and related oils. Apart from renieratane and isorenieratane, 1H NMR analysis established the aromatic substitution pattern of the most abundant component present, which was identified as a diaromatic compound with an unprecedented 2,3,6-/3,4,5-trimethyl aromatic substitution pattern. Molecular and isotopic analyses of both soluble and insoluble fractions of organic matter revealed relationships between diagenetically-derived carotenoids found in bitumen and related oils and their precursors incorporated into high-molecular-weight fractions. Aryl isoprenoids, important components in extracts and oils, were apparently derived from thermal cracking of bound diaromatic carotenoids rather than cleavage of free carotenoids as previously suggested. Furthermore, products derived from diaromatic carotenoids were substantially enriched in 13C relative to n-alkanes of algal origin. Together with the characteristic carotenoids, this isotopic enrichment provides evidence of significant contributions from photosynthetic green sulphur bacteria (Chlorobiaceae), which fix carbon via the reversed tricarboxylic acid (TCA) cycle. In spite of the prominence of these molecular signals, the overall isotopic composition of the organic matter indicated that only a very small portion of the preserved organic carbon was derived from the biomass of photosynthetic green sulphur bacteria.     

Light requirements of the seagrass,Zostera muelleri,determined by observations at the maximum depth limit in a temperate estuary,New Zealand

The Kaipara Harbour in New Zealand is one of the largest estuarine systems in the world, containing significant areas of subtidal seagrass habitat (Zostera muelleri). Light availability at the maximum depth limit for Z. muelleri was measured at 2.10 (0.19 SEM) and 4.91 (0.53 SEM) mol photons m^?2 d^?1 during the winter and summer monitoring periods, respectively. The primary drivers of benthic light availability were found to be surface light availability, the timing of the low tide and water clarity. Core sampling analysis suggested that biomass of seagrass growing at the maximum depth limit was low, indicative of light limitation. The results of this study suggest that the subtidal distribution of seagrass in the Kaipara Harbour is light-limited and that reductions in water clarity due to changes in land use are likely to result in significant reductions in the extent and productivity of subtidal seagrass habitat.     

Characterization of hydrocarbons in a subsurface oil-rich layer in the Sargasso Sea

The hydrocarbon composition of seawater samples collected within a subsurface oil-rich layer in the southwest North Atlantic Ocean (Sargasso Sea) during February–March, 1978, has been examined in detail. Chromatograms generated through gas chromatographs/mass spectrometry (GC/MS) analyses of saturated and aromatic hydrocarbons are characterized by a narrow unresolved envelope (UCM or unresolved complex mixture) containing isoprenoids as major resolved peaks, suggesting a petroleum source which has undergone moderate biodegradative weathering. Distributions of terpanes, steranes and polycyclic aromatic hydrocarbons corroborate the inferred fossil origin. Stable carbon isotopic compositions (δ¹³C) suggest that the source of these hydrocarbons is enriched in ¹³C in comparison with most petroleums. The results support the previous suggestions (Harvey et al., 1979) that this layer is part of a massive submarine oil seep originating somewhere on the Venezuelan shelf, although its origin cannot be attributed to seepage of a specific oil formation.     

Organic geochemistry of sediments from chemosynthetic communities,Gulf of Mexico slope

We used a research submersible to obtain 33 sediment samples from chemosynthetic communities at 541–650 m water depths in the Green Canyon (GC) area of the Gulf of Mexico slope. Sediment samples from beneath an isolated mat of H₂S-oxidizing bacteria at GC 234 contain oil (mean = 5650 ppm) and C₁–C₅ hydrocarbons (mean = 12,979 ppm) that are altered by bacterial oxidation. Control cores away from the mat contain lower concentrations of oil (mean = 2966 ppm) and C₁–C₅ hydrocarbons (mean = 83.6 ppm). Bacterial oxidation of hydrocarbons depletes O₂ in sediments and triggers bacterial sulfate reduction to produce the H₂S required by the mats. Sediment samples from GC 185 (Bush Hill) contain high concentrations of oil (mean = 24,775 ppm) and C₁–C₅ hydrocarbons (mean = 11,037 ppm) that are altered by bacterial oxidation. Tube worm communities requiring H₂S occur at GC 185 where the sea floor has been greatly modified since the Pleistocene by accumulation of oil, thermogenic gas hydrates, and authigenic carbonate rock. Venting to the water column is suppressed by this sea-floor modification, enhancing bacterial activity in sediments. Sediments from an area with vesicomyid clams (GC 272) contain lower concentrations of oil altered by bacterial oxidation (mean = 1716 ppm) but C₁–C₅ concentrations are high (mean = 28,766 ppm). In contrast to other sampling areas, a sediment associated with the methanotrophic Seep Mytilid I (GC 233) is characterized by low concentration of oil (82 ppm) but biogenic methane (C₁) is present (8829 ppm).     

Feasibility of co-culture of the Australasian sea cucumber (Australostichopus mollis) with the Pacific oyster (Crassostrea gigas) in northern New Zealand

The Australasian sea cucumber (Australostichopus mollis) has attracted commercial attention for aquaculture development, partly due to its potential for co-culture with shellfish and finfish species. However, minimal attention has been given to the possibility of co-culturing this species with oysters. In this study we evaluated the growth of juvenile sea cucumbers (36.7 ± 0.9 g, wet weight) caged underneath Pacific oyster farms in northern New Zealand. Co-culture started at the end of the summer, and after 304 days the juveniles had doubled in size (79.8 ± 3.3 g, wet weight), but their subsequent growth appeared to be constrained by overstocking of the cages and summer water temperatures, reaching a carrying capacity of 720 g m^?2. Overall, the results of this study indicate that the co-culture of juvenile sea cucumbers with Pacific oysters is feasible, if sea cucumber losses are reduced (between 33% and 52% lost in this study) and careful attention is given to stocking rates and the water temperature regimes of oyster farms in order to maintain adequate growth rates.     

Geochemistry of C25 and C30 biogenic alkenes in sediments of the narragansett bay estuary

The distributions of a series of structurally related C₂₅ and C₃₀ biogenic alkenes in sediments of the Narragansett Bay estuary have been determined. The suite of alkenes detected differs both quantitatively and qualitatively from those previously reported in other estuanne and coastal regions. Four C₂₅ mono- and dienes and one C₃₀ diene comprise 73–91% of the total alkenes in all surface (upper 2.5–5 cm) sediments analyzed. However, significant geographic variations exist in the relative abundance of these five compounds throughout the estuary. A comparison of alkene concentrations with δ¹³C of the bulk sedimentary organic matter has shown that the geographic variations of some alkenes reflect the distribution of marine organic matter, suggesting a marine source for these compounds. The distributions of other alkenes are not similarly correlated. In particular, concentrations of the C₃₀ diene are relatively constant and exhibit no dependence on the origin of organic matter in these sediments. This distribution implies an in situ production of this alkene throughout the estuary. Analysis of several sediment cores reveals that alkene concentrations are generally highest at the surface and decrease to low, constant values within the upper 25 cm. An exception is the subsurface concentration of one C₂₅ diene, which exhibits an increase at the same depth in two separate upper bay cores.