In this issue

Abstract

IN THIS ISSUE Bruce Osborne Reef Decline When I think of reefs, a vision of a warm tropical paradise often springs to mind. Whilst these coraldominated reefs, comprised largely of small marine invertebrates that secrete an exoskeleton of calcium carbonate, are globally the most significant, other reefs that are not as well-known as their tropical cousins can be found in cooler temperate locations. Reefs come in a range of shapes and sizes and are generally considered to consist of rocky concretions that rise from the sea bed. There are two major types, one where the structure is created by animals, called biogenic reefs and one where the animal and plant communities are found growing on raised inanimate material. One such biogenic reef that is found in temperate waters is largely made up of the Horse Mussel, Modiolus modiolus. In Strangford Lough (Northern Ireland), reefs dominated by M. modiolus were formerly quite common but, as Strong et al., in this issue, show there has been a dramatic decline in this reef type over the last 40 years, with the area occupied reduced by 37% and the abundance by 87%. Trawling for scallops, predation and environmental change are all proposed as factors that could have contributed to this decline, although the evidence for any of these is equivocal. Given the importance of M. modiolus, as a filter feeder, in maintaining water clarity as well as having an important role in nutrient cycling, this decline could have a large impact on primary production and ecosystem functioning. As the authors point out, however, unless we know exactly the reason(s) for the decline, the implementation of any conservation measures is fraught with difficulty. Benthic fish and sea urchins in Lough Hyne Lough Hyne, Europe’s first marine reserve and is still the only one in Ireland, has been the focus of extensive research since the 1930s. Despite the extensive research, however, the role of fishes in the benthic and pelagic food webs within the Lough has received little attention. This is of particular concern due to recent changes in the Lough, including elevated nutrient concentrations, modified oxygen concentrations and the increased mortality of the purple urchin, which is regarded as a keystone species. The decline in the sea urchin populations since the 1990s has often been assumed to be due to increased predation by benthic fishes, which are known to be potential predators. However, this earlier suggestion is largely refuted by Jiole et al., in this issue, who base their argument on an analysis of fish gut contents and point out that there is also little direct evidence of predation before or after the 1980s. So what is the cause of the decline in sea urchins? Again, we are left with a conundrum. In terms of fish populations, all the factors examined, including site, tidal effects and weather conditions had an impact, as could the marked changes in the environmental conditions in the Lough. Perhaps the markedenvironmental changesunderliethe demise of the sea urchin, but to what extent is unclear and warrants further investigation. A top oomycete Losses due to plant disease probably result in a 40% reduction in the productivity of the six most important food crops. Of these plant diseases, infestations by the oomycete pathogen Phytophthora are particularly significant, with a recent survey listing six species as being in the top ten of oomycete pathogens globally. Traditionally, species from the Phytophthora genus were classified as fungi, although molecular analyses suggest that they have attributes that are related more to golden brown algae and diatoms rather than true fungi. Their effect on plant health in Ireland has been significant, influencing both agriculture and forestry and, by all accounts, this impact is likely to increase given increased globalisation in the international trade in plants and plant-related commodities as well as through changes in climate. O’Hanlon et al., in this issue, reflect on the evidence for the increased impact of Phytophthora and other disease-causing microorganisms , which comes at a time of declining expertise and investment in plant pathology and mycology. O’Hanlon et al. use published and unpublished records to review the occurrence and ecology of Phytophthora species on this Island, paying...