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Final Activity and Management Report Summary - PHENOMED (Climate change, phenology and reproduction: Mediterranean sponges as models)

Potential effects of global change act at different organisation levels from physiological to community and can ultimately lead to a significant diversity loss and affect ecosystem functioning. Phenology - the timing of seasonal activities of organisms - is perhaps the simplest process which would detect changes in the ecology of species in response to global change. Reproduction in marine invertebrates must be highly synchronised to ensure success. This synchronisation is moderated using external cues and the temperature is the principal variables to which the organism's biology can be linked. If a temperature threshold or change is used as a single cue, this may result in the animal initiating a physiological response at the wrong time.

Although some information on reproductive cycles of Mediterranean marine invertebrates is available, little is known about their reproductive efforts and relationships with environmental fluctuations. There is an urgent need for improving the knowledge on phenology in different ecological conditions, especially for assessing at this level the effect of natural or human-induced perturbations. Therefore, given that sponges are major components in many marine communities, it remains important to assess their phenology, with special attention to climate-driven shifts in reproductive processes that may alter recruitment and population structure.

The general aim of the programme PHENOMED was to contribute to a better understanding of the impact of strong disturbances linked to global change on the life/reproductive cycles and embryonic development using several sponge species with different temperature sensitivity and tolerance from different ecological conditions as models in order to provide management and conservation advices.

We detected that the sex ratio can be affected by temperature fluctuations, especially for species with seasonal reproductive cycles (Oscarella lobularis, O. tuberculata, O. balibaloi). Reproductive efforts (the parental contribution in every act of reproduction) of O. tuberculata, O. lobularis and O. balibaloi are variable in time and according to the sex considered. The maximal effort of O. tuberculata, O. lobularis is usually observed between July and August and in O. balibaloi between April and June for both sexes when the seawater temperature starts to increase. The same correlation has been detected in commercial sponges Spongia officinalis, characterised by a continual reproduction, but with two peaks of effort per year and Hippospongia communis. So whatever the seasonality of the reproduction, there is positive correlation between the rising of the seawater temperature and increasing of the reproductive effort in both sexes. In Oopsacas minuta - the cold stenotherm model which only lives in cold Mediterranean environment - there is no considerable difference of the reproductive effort all during the year. Thus, the timing of reproductive cycle events became a good indicator of climate change and first of all, temperature change, due to its sensitivity and dependence facing several climate variables. Moreover, the temperature triggers and controls key stages of sponge's reproduction such as gametogenesis and larval release.

The global warming may have significant impacts on the reproductive success of a wide range of marine invertebrates. It can reduce reproductive fitness, may relate to altered sex ratio, to reduced fecundity as a consequence of incomplete gametogenesis, complete/partial failure to spawning at an inappropriate time, thereby reducing larval survival. However, climate change will likely induce a reduction in invertebrate fecundity and recruitment, especially for species which synchronise their reproduction with environmental fluctuations.

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