Ocean warming and tropical invaders erode the performance of a key herbivore.

Climate change and bioinvasions are two facets of global change that can act in tandem to impact native species and ecosystems. However, their combined effects on key species have rarely been studied. The Mediterranean Sea is a hot spot of both ocean warming and bioinvasions, where their impact can be tested together. In recent years, the population of a key herbivore, the European purple sea urchin (Paracentrotus lividus), has virtually collapsed along the Israeli Mediterranean coast (southeastern Levant). Here, we used field and lab experiments to test two complementary hypotheses that may explain the urchin population collapse: (1) resource competition that may lead to competitive exclusion by invasive grazers (two Red Sea rabbitfishes) and (2) reduced performance due to ocean warming. An inclusion-exclusion in situ caging experiment revealed a strong negative impact of fish grazing on algal cover and on the urchin's gut content and gonado-somatic index (GSI). Laboratory experiments revealed a considerable negative impact of both elevated temperature and food deficiency on sea urchin respiration and GSI, and consequently on its energy budget and reproductive potential and, potentially, fitness. Such reduced reproductive capacity must have greatly lowered the sea urchin's population viability, contributing (and possibly even leading) to its collapse in the southeastern Levant in the past two decades. Urchin population declines are expected to spread to the west and north of the Mediterranean Sea following further warming and rabbitfish expansion. This study is the first to demonstrate the potential additive effects of ocean warming and implied competitive exclusion by an invader on a native species at its warm biogeographic distribution edge.

Particulate organic matter as a food source for a coral reef sponge.

The ability of sponges to feed in diverse (including oligotrophic) ecosystems significantly contributes to their ubiquitous aquatic distribution. It was hypothesized that sponges that harbour small amounts of symbiotic bacteria in their mass feed mainly on particulate organic matter (POM). We examined the nearly symbiont-free (by microscopic observation) filter-feeding Red Sea sponge Negombata magnifica in order to: (a) study removal efficiency of naturally occurring organic particles, (b) measure the total amount of absorbed particulate organic carbon (POC) and nitrogen (PON), and (c) estimate organic carbon and nitrogen flux in this sponge. Total amount of organic carbon and nitrogen in the Gulf of Aqaba was found to be 48.46+/-5.69 microg l(-1) and 6.45+/-0.7 microg l(-1), respectively. While detritus contributed 54% of POC, most PON (84%) came from planktonic microorganisms, mainly prokaryotes. Particle removal efficiency ranged from 99% (the cyanobacterium Synechococcus sp.) to 37% (for eukaryotic cells >8 microm). On average, N. magnifica ingested 480 microg C day(-1) g(-1) (wet mass, WM) sponge and 76.6 microg N day(-1) g(-1) sponge. Ingested POC balanced 85% of the sponge's energetic demand but more is needed for biomass production because it cannot digest all of the carbon. 54.4+/-16.1 microg N day(-1) g(-1) (WM) nitrogen was excreted as total ammonia nitrogen (TAN); however, nitrogen allowance should be higher because more nitrogen is deposited for sponge biomass during growth. It is hypothesized that the discrepancy in the nutritional requirements should be covered by the sponge absorbing carbon and nitrogen from sources that are not dealt with in the present research, such as dissolved organic carbon and nitrogen. This study highlights the significance of detritus as a carbon source, and prokaryotes as a PON source in sponge feeding.

Lack of benefit of early awareness to age-related macular degeneration.

AIMS: To assess the rate of early awareness to the presence of age-related macular degeneration (AMD) and whether it enables early detection of transition to neovascular AMD (NVAMD) as compared with patients whose first presentation to an ophthalmologist is already at the neovascular stage of disease. METHODS: A retrospective analysis of 268 eyes of 268 consecutive patients with newly diagnosed NVAMD that were treated in a tertiary referral centre was performed. Patients were classified into those who were unaware (Group 1), or aware (Group 2), of the fact that they had AMD before diagnosis of NVAMD. Visual acuity, lesion size and composition, and demographics were compared between both groups. RESULTS: In all, 185 patients (69%) and 83 patients (31%) were classified to Groups 1 and 2, respectively. Patients in Groups 1 and 2 had similar demographic characteristics, presenting visual acuity and lesion size, and lesion compositions. Group 1 patients were more likely to have a positive history for smoking (41 vs26% in Group 2, P=0.03), whereas Group 2 patients were more likely to have positive family history for AMD (20 vs10%, P=0.02). CONCLUSIONS: These data suggest that current screening methods fail to identify the majority of patients with AMD before the development of NVAMD. The findings also demonstrate that in the routine clinical setting, prior awareness of AMD may not facilitate early detection of treatable choroidal neovascularization lesions.