Enhanced ROV Survey of Tropical Fish and Benthic Communities Associated With Shallow Oil and Gas Platforms

Understanding the ecology of oil and gas infrastructure in our oceans is required to inform decommissioning such that environmental impacts are minimised, and benefits maximised. This study equipped an industrial remotely operated vehicle (ROV) with a stereo-video system and collected seven hours of high-definition imagery of two platform jackets, for assessments of benthic (type, density, complexity) and fish assemblages (richness, abundance, length) present. Harriet Alpha (25 m depth) and Gibson/South Plato (8 m depth) are located ca. 120 km offshore of north-west Australia, adjacent to Varanus Island. Twenty-one ‘classes’ of benthic biota were observed in high density, with little bare structure on either platform. Encrusting sponges (average 19% cover per virtual quadrat), barnacles (17%) and sponges (16%) were common on Gibson/South Plato while encrusting sponges (16%) and macroalgae (18%) were ubiquitous on quadrats on Harriet Alpha. The sun coral Tubastraea faulkneri was common on Harriet Alpha (38% of quadrats), though coverage was low (<6%). A total of 102 fish species from 27 families were observed. This included 33 fishery target species with an estimated relative mass of 116 kg on Gibson/South Plato and 299 kg on Harriet Alpha, with these species typically concentrated near the seafloor-structure interface. Differences in benthic biota communities present on each platform likely reflect spatial variations in oceanographic processes, proximity to natural habitats and the age, configuration, cleaning regime and depth of the structures themselves. This study demonstrates the value of adding stereo-video systems to ROVs to undertake rapid scientific surveys of oil and gas infrastructure.

Implications of 2D versus 3D surveys to measure the abundance and composition of benthic coral reef communities

A paramount challenge in coral reef ecology is to estimate the abundance and composition of the communities residing in such complex ecosystems. Traditional 2D projected surface cover estimates neglect the 3D structure of reefs and reef organisms, overlook communities residing in cryptic reef habitats (e.g., overhangs, cavities), and thus may fail to represent biomass estimates needed to assess trophic ecology and reef function. Here, we surveyed the 3D surface cover, biovolume, and biomass (i.e., ash-free dry weight) of all major benthic taxa on 12 coral reef stations on the island of Curaçao (Southern Caribbean) using structure-from-motion photogrammetry, coral point counts, in situ measurements, and elemental analysis. We then compared our 3D benthic community estimates to corresponding estimates of traditional 2D projected surface cover to explore the differences in benthic community composition using different metrics. Overall, 2D cover was dominated (52 ± 2%, mean ± SE) by non-calcifying phototrophs (macroalgae, turf algae, benthic cyanobacterial mats), but their contribution to total reef biomass was minor (3.2 ± 0.6%). In contrast, coral cover (32 ± 2%) more closely resembled coral biomass (27 ± 6%). The relative contribution of erect organisms, such as gorgonians and massive sponges, to 2D cover was twofold and 11-fold lower, respectively, than their contribution to reef biomass. Cryptic surface area (3.3 ± 0.2 m2 m−2planar reef) comprised half of the total reef substrate, rendering two thirds of coralline algae and almost all encrusting sponges (99.8%) undetected in traditional assessments. Yet, encrusting sponges dominated reef biomass (35 ± 18%). Based on our quantification of exposed and cryptic reef communities using different metrics, we suggest adjustments to current monitoring approaches and highlight ramifications for evaluating the ecological contributions of different taxa to overall reef function. To this end, our metric conversions can complement other benthic assessments to generate non-invasive estimates of the biovolume, biomass, and elemental composition (i.e., standing stocks of organic carbon and nitrogen) of Caribbean coral reef communities.

Processing of Naturally Sourced Macroalgal- and Coral-Dissolved Organic Matter (DOM) by High and Low Microbial Abundance Encrusting Sponges

Sponges play a key role in (re)cycling of dissolved organic matter (DOM) and inorganic nutrients in coral reef ecosystems. Macroalgae and corals release different quantities of DOM and at different bioavailabilities to sponges and their microbiome. Given the current coral- to algal-dominance shift on coral reefs, we assessed the differential processing of macroalgal- and coral-DOM by three high and three low microbial abundance (HMA and LMA) encrusting sponge species. We followed the assimilation of naturally sourced 13C- and 15N-enriched macroalgal- and coral-DOM into bulk tissue and into host- versus bacteria-specific phospholipid fatty acids (PLFAs). Additionally, we compared sponge-processing of the two natural DOM sources with 13C- and 15N-enriched laboratory-made diatom-DOM. All investigated sponges utilized all DOM sources, with higher assimilation rates in LMA compared to HMA sponges. No difference was found in carbon assimilation of coral- versus macroalgal-DOM into bulk tissue and host- versus bacteria-specific PLFAs, but macroalgal nitrogen was assimilated into bulk tissue up to eight times faster compared to the other sources, indicating its higher bioavailability to the sponges. Additionally, LMA sponges released significantly more inorganic nitrogen after feeding on macroalgal-DOM. Therefore, we hypothesize that, depending on the abundance and composition of the sponge community, sponges could catalyze reef eutrophication through increased turnover of nitrogen under coral-to-algal regime shifts.

Changes and stability of a Mediterranean hard bottom benthic community over 25 years

During the last decades, the Mediterranean shallow-water benthic communities have experienced significant changes in taxa composition and distribution. These variations were related to a complex set of anthropogenic stressors as well as to mass mortality events starting from 1999 and related to the current climatic changes. To evaluate the effect of these changes on long-living species with a limited larval dispersal capacity, a quantitative and qualitative monitoring of the shallow-water hard bottom community structure was performed over a pluri-decennial interval of time. The aim of this work was the comparison of the quali-quantitative occurrence and seasonal cycles of several benthic taxa living on a rocky cliff of the Portofino Promontory (eastern Liguria, Mediterranean Sea), from 15 to 20 m depth. The studied community, within a Lithophyllo–Halimedetum tunae association, was analysed by sets of photographs repeated, exactly in the same site, at 25 years of distance (1987/88 and 2012/13). The results suggest that the macroalgal coverage of the surveyed cliff suffered, during the monitored span of time, a significant depletion in quali-quantitative terms, while the overall sponge coverage remained almost unvaried. Nevertheless, a discrete analysis of the most common sponge species present in the study area showed significant variations, with some taxa now more abundant (Axinella spp. and Agelas oroides), some virtually stable (Cliona viridis and the complex of red encrusting sponges), and others drastically depleted (Chondrosia reniformis, Phorbas tenacior, Acanthella acuta, Ircinia spp., Dysidea avara and Petrosia ficiformis). Finally, some sponge species showed clear seasonal cycles indicating recruitment periods and post-recruit mortalities.

Benthic Egg Masses and Larval Development of Amblyosyllis Speciosa (Polychaeta: Syllidae)

Eggs of the syllid polychaete Atnblyosyllis speciosa are deposited in benthic gelatinous masses. Embryos and larvae develop within these masses until about three weeks after fertilization, after which they crawl or swim away and metamorphose. Only one other syllid, the Mediterranean Syllides edentula, has been reported to form benthic egg masses.While some syllid polychaetes spawn gametes freely into the water column where they are fertilized and develop without additional parental care, most species protect developing embryos in some fashion. Four modes of brood protection have been reported in the syllids. Protection of embryos within the ventral brood chamber of a planktonic adult is characteristic of members of the subfamily Autolytinae, and of some members of the Eusyllinae (Garwood, 1991). Physical attachment of embryos to the body of the maternal parent (external gestation) occurs in all members of the Exogoninae and in a few eusyllines (Heacox & Schroeder, 1978; Garwood, 1991). Viviparity is less common, having been reported in a few species in the subfamily Syllinae (Schroeder & Hermans, 1975; Ben-Eliahu, 1975) and in one exogonine (Pocklington & Hutcheson, 1983). Finally, the formation of benthic egg masses has been described in only one species, the eusylline Syllides edentula Claparède (Cognetti-Varriale, 1971).In this study the benthic egg masses and development of another eusylline, Amblyosyllis speciosa Izuka, 1912, are described. In December 1995, at the Friday Harbor Laboratories (FHL), Washington, USA, five adult worms were found on a bivalve shell heavily infested with the boring sponge Cliona sp. Additional specimens and egg masses were collected in June 1996 and April-June 1997 from encrusting sponges on the FHL breakwater.

Encrusting organisms on co-occurring disarticulated valves of two marine bivalves: comparison of living assemblages and skeletal residues

Study of the assemblage of encrusting organisms on co-occurring disarticulated valves of the bivalves Crassostrea virginica and Mercenaria mercenaria in Bogue Sound, North Carolina, indicates that there is little or no substrate specificity among the encrusting organisms but that the shape of the shells has an important influence on how extensively members of each higher taxon collectively inhabit the shells. Encrusting bryozoans, a dense low mat composed of many species from diverse phyla, and a unicellular film cover most of the area of both exterior and interior surfaces. The encrusting bryozoans most extensively cover both surfaces of C. virginica but are in second place behind the multispecies mat on exterior surfaces of M. mercenaria and behind the unicellular film on its interior surfaces. These differences are inferred to result from different physical stability of valves of the two bivalve species, which exhibit different frequencies of circumrotatory growth.Degradation of the assemblage by sodium hypochlorite, to simulate loss of organic matter during fossilization, results in the complete loss of encrusting sponges, erect hydrozoans, erect bryozoans, and ascidians. Loss of these taxa results in overexposure and more apparently uniform distribution of skeletal taxa with respect to their surface representation in living assemblages and also in complete loss of the higher tiers present in the living assemblage. However, indications of the original structural organization of the living assemblage is indicated by preservation of the most abundant taxa in the lower tiers and by the retention in the reduced treated assemblage of the patterns of distribution that characterized the living assemblage.

Patterns in sponge (Porifera) assemblages on temperate coastal reefs off Sydney, Australia

Pattern and process in deep-water macrobenthic assemblages have largely been inferred from the study of such assemblages on shaded artificial structures in relatively shallow water. This paper examines patterns in the diversity and abundance of sponges to a depth of 50 m on coastal reefs off Sydney, Australia. Photo-quadrats were used to provide estimates of the species richness and percentage cover of sponges on three reefs. Sponge morphotype (i.e. encrusting or massive) was also recorded. Within-reef variation was examined by nesting three sites within each reef at each of three depths; replicate photo-quadrats (0.45 m², n = 5) were taken at each site. In addition, a remotely operated vehicle was used to collect voucher specimens. Over 50 species of sponge were identified, many of which have never been described. In general, sponge richness increased with depth, as did the number of erect or massive forms. In contrast, cover decreased with depth, particularly for encrusting sponges. Univariate and multivariate analyses revealed considerable small-scale spatial and temporal variation in sponge distribution and abundance. A significant positive relationship between richness and cover was also apparent. In general, there were greater temporal changes in the patterns of abundance for the shallow reef assemblages at 20 m, relative to those at 30 m and 50 m.

Suspended Particulate Loading on the Macrobenthos in a Highly Turbid Fjord: Knight Inlet, British Columbia

Knight Inlet is a deep, low-energy but well-oxygenated fjord. The effects of turbidity are principally those of seasonally very high vertical flux from the sediment-laden surface layer. Submersible observations of the benthos are related to suspended load and sedimentation rate data. The bayhead delta slope receives a continual rain of glacial silt (30 cm/yr) and has summer sedimentation rates of 4 kg∙m−2∙d−1.The epifauna of the steep fjord walls shows a marked down-inlet increase in abundance, and the number of species increases from 9 to 45. Brachiopods (Laqueus californianus), solitary corals (Caryophyllia/Cyathoceros), and encrusting sponges are remarkably tolerant of high turbidity. The high sedimentation rates affect the epifauna in three ways: (1) subjection to the ubiquitous "gentle rain" of floes and agglomerates; (2) more locally, microturbidity flows set off by biological resuspension of unstable slope sediment; and (3) major slides of rock and/or sediment. Submarine soil-creep limits the slope infauna, by burrows requiring repeated reexcavation.Down-inlet decrease in sedimentation rate is accompanied by a change in feeding type. In the upper inlet, suspension feeders taking particles < 8 μm (e.g. sabellids, brachiopods) probably utilize bacteria associated with the high vertical flux of SPM. In the middle inlet, selective suspension feeders (e.g. crinoids, gorgonians) sort the SPM for larger particles. In the lower inlet, filter feeders (e.g. barnacles, glass sponges) increase, especially where currents are stronger. The soft-bottom detritus feeders also show a change: from epibenthic forms (e.g. pandalid shrimp, spider crabs) in the upper inlet, through burrowing shrimp in the middle inlet, to ophiuroids in the lower inlet. These changes are correlated with the greater amounts of organic carbon preserved in bottom sediments as they are less diluted by glacially derived inorganic material.The modern-day "turbid association" of brachiopods, solitary corals, and sponges recalls typical outer shelf-basinal shale facies of the Palaeozoic. Turbid, low-energy environments were thus colonized early but faunas have since become less diverse.Key words: fjord, benthos, sedimentation, submersible