Effects of suspended sediments,dissolved inorganic nutrients and salinity on fertilisation and embryo development in the coral <Emphasis Type=Italic>Acropora millepora</Emphasis> (Ehrenberg, 1834)

Exposure of coral reefs to river plumes carrying increasing loads of nutrients and sediments is a pressing issue for coral reefs around the world including the Great Barrier Reef (GBR). Laboratory experiments were conducted to investigate the effects of changes in inorganic nutrients (nitrate, ammonium and phosphate), salinity and various types of suspended sediments in isolation and in combination on rates of fertilisation and early embryonic development of the scleractinian coral Acropora millepora. Dose–response experiments showed that fertilisation declined significantly with increasing sediments and decreasing salinity, while inorganic nutrients at up to 20 μM nitrate or ammonium and 4 μM phosphate had no significant effect on fertilisation. Suspended sediments of ≥100 mg l⁻¹ and salinity of 30 ppt reduced fertilisation by >50%. Developmental abnormality occurred in 100% of embryos at 30 ppt salinity, and no fertilisation occurred at ≤28 ppt. Another experiment tested interactions between sediment, salinity and nutrients and showed that fertilisation was significantly reduced when nutrients and low concentrations of sediments co-occurred, although both on their own had no effect on fertilisation rates. Similarly, while slightly reduced salinity on its own had no effect, fertilisation was reduced when it coincided with elevated levels of sediments or nutrients. Both these interactions were synergistic. A third experiment showed that sediments with different geophysical and nutrient properties had differential effects on fertilisation, possibly related to sediment and nutrient properties. The findings highlight the complex nature of the effects of changing water quality on coral health, particularly stressing the significance of water quality during coral spawning time. Communicated by Environment Editor Professor Rob van Woesik     

Complementary (secondary) metabolites in an octocoral competing with a scleractinian coral: effects of varying nutrient regimes

Competitive interactions between two sessile, epibenthic species were investigated on the Great Barrier Reef (GBR) in the presence and absence of added nutrients, as part of the Enrichment of Nutrients on Coral Reefs Experiment (ENCORE). Sarcophyton ehrenbergi Marenzeller (Octocorallia: Alcyonacea), an alcyonacean soft coral, and Pocillopora damicornis (Linnaeus), a scleractinian coral, were relocated and placed in contact with each other on large plastic grids on each of 12 micro-atolls within the One Tree Island (OTI) lagoon (23°30′S, 152°96′E, GBR). These micro-atolls were allocated in equal-sized groups to three enrichment treatments (addition of nitrogen, N; addition of phosphorus, P; addition of both nitrogen and phosphorus, N+P) and one control. Non-relocated (NR) and relocated colonies were also monitored as controls. After relocation and 1 year of nutrient enrichment, concentrations of a terpenoid complementary metabolite—sarcophytoxide—and wax esters were analyzed in colonies of S. ehrenbergi that had been exposed to elevated concentrations of N, P, N+P and compared with colonies on the non-nutrient-enriched control. Non-relocated control colonies from the natural environment were monitored over a period of 1 year and compared to colonies relocated to the control micro-atolls to assess handling effects. Analyses were performed on non-interacting S. ehrenbergi colonies, S. ehrenbergi colonies in experimental contact with P. damicornis colonies, and on non-interacting S. ehrenbergi colonies from the site of initial collection. Significant differences were found between sarcophytoxide levels in colonies of S. ehrenbergi in contact with P. damicornis vs. control/non-contact colonies; contact colonies had higher levels of this metabolite. Non-relocated control colonies of S. ehrenbergi exhibited significantly higher levels of sarcophytoxide than relocated control colonies. Augmentation of nutrient levels in micro-atolls significantly increased sarcophytoxide levels in S. ehrenbergi colonies relative to colonies on the control micro-atolls, although this response was not strong. Concentrations of fatty esters increased significantly through time in S. ehrenbergi colonies in their natural setting (non-relocated controls). This variability was not observed in relocated colonies in the treatment and control micro-atolls, irrespective of contact with P. damicornis. Concentrations of fatty esters in colonies of S. ehrenbergi in contact with P. damicornis were significantly lower than control/non-contact colonies, indicating that there is a cost in terms of stored energy reserves for the production of additional complementary metabolites when involved in competition for space. Augmentation of P levels in micro-atolls induced significant increases in fatty ester levels within S. ehrenbergi colonies vs. colonies in control micro-atolls, or in micro-atolls treated with added N or N+P together. These findings indicate that interspecific competition for space between a scleractinian coral and an alcyonacean soft coral and/or changes in the environmental nutrient regime can influence concentrations of complementary/secondary metabolites in the alcyonacean coral and the organism's stored energy reserves.     

Coral reef encruster communities and carbonate production in cryptic and exposed coral reef habitats along a gradient of terrestrial disturbance

Encrusting calcareous organisms such as bryozoans, crustose coralline algae (CCA), foraminiferans, and serpulid worms are integral components of tropical framework-building reefs. They can contribute calcium carbonate to the reef framework, stabilise the substrate, and promote larval recruitment of other framework-building species (e.g. coral recruits). The percentage cover of encrusting organisms and their rates of carbonate production (g m⁻² year⁻¹) were assessed at four sites within a coastal embayment, along a gradient of riverine influence (high-low). As the orientation and type of substrate is thought to influence recruitment of encrusting organisms, organisms recruiting to both natural (the underside of platy corals) and experimental substrates were assessed. The effect of substrate exposure under different levels of riverine influence was assessed by orientating experimental substrates to mimic cryptic and exposed reef habitats (downwards-facing vs upwards-facing tiles) at each site. Cryptic experimental tiles supported similar encruster assemblages to those recruiting to the underneath (cryptic side) of platy corals, suggesting that tiles can be used as an experimental substrate to assess encruster recruitment in reef systems. Encruster cover, in particular CCA, and carbonate production was significantly higher at low-impact (clear water), high wave energy sites when compared to highly riverine impacted (turbid water), low wave energy sites. Cryptically orientated substrates supported a greater diversity of encrusting organisms, in particular serpulid worms and bryozoans. The inverse relationships observed between riverine inputs and encrusters (total encruster cover and carbonate production) have implications for both the current and future rates and styles of reefal framework production.     

Temporal variations in phytoplankton, particulates, and colored dissolved organic material based on optical properties during a Long Island brown tide compared to an adjacent embayment

Since 1985, the coastal embayments of Long Island, New York, have been plagued with recurrent blooms, aptly called brown tides, of the pelagophyte Aureococcus anophagefferens. The distinct ocean color observed during these blooms suggests that optical methods can be used as a tool to study, detect, and track brown tides. Thus, the goal of our project was to compare the optical properties and pigment composition during bloom and non-bloom conditions and assess temporal variations in the phytoplankton and other constituents in the seawater associated with bloom development. From 17 May to 8 June 2000, we measured a time series of particle size distributions and concentrations as well as size-fractioned algal pigments and optical properties in two Long Island embayments where brown tides are known to occur. During our study, A. anophagefferens represented an insignificant contribution to the algal community in West Neck Bay (WNB), whereas a bloom developed in Quantuck Bay (QB). Initially, temperature and salinity were similar at the two locations; however, bulk optical properties, chlorophyll, and particle concentrations were nearly a factor of 2 greater at QB. Bulk optical properties remained constant at WNB, yet increased exponentially at QB as the bloom developed. The composition of particulates, including phytoplankton, varied little at QB, and the optical properties suggested the dominance of A. anophagefferens (confirmed by microscopy). The largest temporal variations were observed in the colored dissolved organic material (CDOM); the colloidal (0.2–0.7 μm) fraction, exhibiting a strong protein-like signal, increased dramatically at the height of the bloom. At WNB particle sizes and algal composition varied despite the invariant bulk optical properties; CDOM variations were minimal. Overall, the optical properties in the two bays demonstrated that at QB temporal variations were dominated by biomass and colloidal protein changes, whereas shifts in the algal community occurred at WNB. This study demonstrates the utility of in situ optical observations to resolve temporal changes in the ecological conditions associated with algal bloom development.