An understanding of the origin and fate of organic matter deposited on the seabed in the Chukchi Sea is critical to our understanding of how regional changes in climate will affect this highly productive ecosystem. We measured the concentrations of chlorophyll a, pheopigments, and accessory pigments in sediments at 39 stations using high-performance liquid chromatography (HPLC) to investigate the degradation pathways of chlorophyll-containing organic matter. Chlorophyll a concentrations were among the highest ever reported in marine sediments (up to 665 mg m -2 ). Measurements of pheopigments, including pheophytin a, pheophorbide a, and pyropheophorbide a, revealed substantial degradative processing of organic matter that began 2 weeks after ice breakup. However, the ratio of chlorophyll a to total pheopigments (Chl a : pheo) was > 1 in most stations, indicating that chlorophyll a was preserved despite grazing and senescent degradation pathways that produced accumulated pheopigments. Increased d 13 C values of bulk sediment organic matter was also positively correlated to concentrations of pheophytin a (p < 0.01, r50.46), and total pheopigment concentration was correlated to the d 13 C values of the epibenthic scavenging snow crab Chionoecetes opilio (p < 0.01, r 5 0.92) and the surface deposit feeding bivalves Macoma spp. (p < 0.01, r 5 0.69). Based on these observations, we hypothesize that organic matter degraded by microbial and herbivorous grazing pathways produces an enriched 13 C signal that is transferred to macrofaunal consumers, providing a critical source of carbon to a rich and diverse benthic food web.

Palmaria decipiens (Reinsch) R.W. Ricker (1987) represents one of the dominant rhodophyte species in Antarctic coastal ecosystems. Due to its high abundance in the intertidal and upper subtidal it plays a key role in ecosystem structure and function, providing habitat, food and shelter for a multitude of associated organisms. The physiology, reproductive strategy and life cycle of P. decipiens is considered as being well adapted to the Antarctic environment, which is characterized by permanent low water temperatures and a strong seasonality in light climate. With its obvious ecological significance and adaptive strategies P. decipiens was frequently studied as a typical representative of an endemic Antarctic macroalga. Here we provide an overview of the recent literature, summarizing the knowledge gained about the alga during the last 25 years. This review focuses on the species life cycle and physiological responses, such as temperature requirements, photosynthetic characteristics, pigment content and protective mechanisms with regard to enhanced ultraviolet radiation (UV-B radiation, 280-315 nm and UV-A radiation, 315-400 nm). The ecology of P. decipiens is reviewed focussing on grazing activity and abundance patterns. Since most studies on P. decipiens have been conducted at King George Island off the western Antarctic Peninsula this overview serves as a summary of baseline data from an ecosystem particularly prone to environmental change.

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Most macroalgal species along the Western Antarctic Peninsula (WAP) are defended against predation, many using chemical defenses. These subtidal communities are also mostly devoid of free living filamentous algae. However, one endo/epiphyte, Elachista antarctica, is found growing exclusively out of the palatable rhodophyte Palmaria decipiens. To understand this unusual and exclusive epiphytization, we tested whether macroalgal secondary metabolites such as those responsible for deterring sympatric grazers, affect the behaviors of the epiphyte's spores. Settlement, germination, and swimming behaviors of the epiphyte's motile spores were quantified in the presence of fractionated lipophilic and hydrophilic extracts of host P. decipiens and other rhodophytes from the shallow subtidal. Host P. decipiens was the only alga tested that did not inhibit spore settlement or germination. We also examined whether extracts from these chemically rich algae affect spore swimming behaviors and found spores to be chemotactically attracted to seawater soluble extract fractions of host P. decipiens. These results indicate that chemosensory behaviors of the epiphyte's spores to metabolites associated with these chemically defended macrophytes can explain this exclusive epiphyte-host interaction.

Eutrophication of coastal waters often leads to excessive growth of microalgal epiphytes attached to seagrass leaves; however, the effect of increased nutrient levels on sediment microalgae has not been studied within seagrass communities. A slow-release NPK Osmocote fertilizer was added to sediments within and outside beds of the shoal grass Halodule wrightii, in Big Lagoon, Perdido Key, Florida. Gross primary production (GPP) and biomass (HPLC photopigments) of sediment microalgae within and adjacent to fertilized and control H. wrightii beds were measured following two 4-week enrichment periods during June and July 2004. There was no effect of position on sediment microalgal GPP or biomass in control and enriched plots. However, nutrient enrichment significantly increased GPP in both June and July. These results suggest that sediment microalgae could fill some of the void in primary production where seagrass beds disappear due to excessive nutrient enrichment. Sedimentary chl a (proxy of total microalgal biomass) significantly increased only during the June enrichment period, whereas fucoxanthin (proxy of total diatom biomass) was not increased by nutrient enrichment even though its concentration doubled in the enriched plots in June.