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Kelp, seaweeds of the order Laminariales, are of ecological and conservation importance because they form undersea forest habitat for many varieties of fauna and flora including mammals, and commercial fish species. In the absence of a world map of the kelp biome, we predicted its potential distribution using geographic records and environment variables in a MaxEnt model. This estimated that the kelp biome occupied 1,469,900 km2 and was present on 22% of the world's coastline. While average sea surface temperature was the most important environmental variable for the biome across all species, wave height, distance from the coast and minimum temperature were of most importance for individual species. This map can be used in planning where marine reserves should be best located, modelling the effects of climate change, and in estimating the blue (ocean) carbon storage. Current field observations should confirm the presence of kelp within the modelled biome, and if absent consider if human impacts, including climate change, are to blame.

A new floristic index, [I/H]RCP, for the estimation of seaweed flora depending on the seawater temperature, is proposed. The index is a ratio of [I]to[H]. [I] is the number of species including both of species with alternation of isomorphic generations and without alternation of generations, and [H] is the number of species including species with alternation of heteromorphic generations, for Chlorophyta, Phaeophyta and Rhodophyta. This new floristic index, [I/H]RCP, clearly demonstrates the positive relationships with seawater temperature which effects the change of seaweed flora.

Halophila decipiens Ostenfeld, a new record for the Hawaiian Islands, was collected from three locations spanning the archipelago: Midway Atoll at 3–15m deep, O’ahu Island at 1–2m deep, and Hawai’i Island at 40m deep. These findings expand the biogeographical distribution of this pantropical seagrass into the north central Pacific Ocean. Specimens showed morphological, reproductive and DNA characteristics typical of the species.

Biogeochemical processes occurring near the sediment–water interface can play an important role in the establishment and persistence of hypoxic-to-anoxic conditions in areas of moderate-to-shallow water depth. Results are given in this paper for diagenetic modeling of two sites from the area on the Louisiana shelf west of the Mississippi River Delta known as the “dead zone”. This is one of the largest and most studied regions where seasonal coastal hypoxia occurs. The diagenetic model was capable of generating good matches with depth profiles at both sites in the upper 8 cm. Moderate differences between predicted and observed concentrations below this depth are most likely due to the highly non-steady state conditions in this region. The model was also able to predict extremely low dissolved sulfide concentrations and bacterial sulfate reduction rates that were in good agreement with independent direct observations. A sensitivity analysis of the model to input parameters showed that the model was much more sensitive to changes in values under hypoxic conditions than norm-oxic or anoxic conditions in the overlying water.

Simulations were carried out to first determine how the profiles of sediment porewater parameters and interfacial fluxes would change under differing quasi-steady state conditions where overlying dissolved oxygen concentrations and the rate of bioirrigation were varied. Next a non-steady state simulation was run to investigate how sediment biogeochemistry would change between these conditions during a hypothetical annual cycle. Results demonstrated a clear need to better understand the dynamic relationship among overlying water oxygen concentrations, the behavior of the benthic faunal community responsible for bioirrigation and sediment biogeochemistry.