Constructing the Suez Canal connected the Red Sea and the Mediterranean Sea, allowing rapid marine bio-invasion. Over the last century, several bivalve species have invaded the Levantine basin, yet their distribution and impact on the benthic community have not been thoroughly studied. Large-scale benthic surveys along the rocky substrate of the Israeli Mediterranean coastline indicate that invading bivalves now dominate the rocky environment, reaching densities of tens to hundreds of individuals per m2. No native bivalve specimens were found in any of the transects surveyed. The small-scale ecological effects of the established invading populations on the benthic community were examined using in-situ exclusion experiment where all invading bivalves were either physically removed or poisoned and kept in place to maintain the physical effect of the shells. Surprisingly, the experimental exclusion showed little measurable effect of bivalve presence on the invertebrate community in close vicinity (~1 m). Bivalves presence had a small, but statistically significant, effect only on the community composition of macroalgae, increasing the abundance of some filamentous macroalgae, and reducing the cover of turf. The generally low impact of invading bivalves could be due to (1) wave activity and local currents dispersing the bivalve excreta, (2) high grazing pressure, possibly by invading herbivorous fish, reducing the bottom-up effect of increased nutrient input by the bivalves, or (3) the natural complexity of the rocky habitat masking the contribution of the increased complexity associated with the bivalve’s shell. We found that established invading bivalves have replaced native bivalve species, yet their small-scale effects on the benthic community seem to be negligible.

The construction of the Suez Canal connected the Red Sea and the Mediterranean Sea, which allowed rapid marine bio-invasion. Over the last century, several bivalve species have invaded the Levantine basin, yet their distribution and impact on the benthic community have not been thoroughly studied. Large-scale benthic surveys along the rocky substrate of the Israeli Mediterranean coastline indicate that invading bivalves, such as Spondylus spinosus , Brachidontes pharaonis, and Pinctada radiata , now dominate the rocky environment, with densities of tens to hundreds of individuals per m 2 . No native bivalve specimens were found in any of the transects surveyed. The small-scale ecological effects of the established invading populations on the benthic community were examined over a year using an in-situ exclusion experiment where all invading bivalves were either physically removed or poisoned and kept in place to maintain the physical effect of the shells. Surprisingly, the experimental exclusion showed a little measurable effect of bivalve presence on the invertebrate community in close vicinity (~ 1 m). Bivalve presence had a small, but statistically significant, effect only on the community composition of macroalgae, increasing the abundance of some filamentous macroalgae and reducing the cover of turf. The generally low impact of bivalves removal could be due to (1) wave activity and local currents dispersing the bivalve excreta, (2) high grazing pressure, possibly by invading herbivorous fish, reducing the bottom-up effect of increased nutrient input by the bivalves, or (3) the natural complexity of the rocky habitat masking the contribution of the increased complexity associated with the bivalve’s shell. We found that established invading bivalves have replaced native bivalve species, yet their exclusion has a negligible small-scale effect on the local benthic community. Supplementary Information The online version contains supplementary material available at 10.1007/s10530-022-02986-1.

Sponges are animals that feed by filtering water through their perforated body. We examined the in situ diel dynamics of sponge metabolism by continuously measuring the oxygen concentrations in the water inhaled and exhaled by undisturbed sponges. A clear daily pattern of oxygen removal was evident for six of the seven species we studied with their nocturnal oxygen removal being almost double the diurnal values (+ 86 AE 57%). Oxygenic photosynthesis by the sponge's symbiotic or endolithic phototrophic microbes may explain some of the diel difference, but significant day-night differences were also observed in three sponge species for which no evidence of photosynthetic activity (tested with imaging pulse-amplitude-modulation Fluorometry) was found. Mean oxygen removal (AE 95% confidence interval for the mean) per species ranged from 1.7 AE 1 μmol O 2 per liter (hereafter: μmol O 2 L À1 ) for the low microbial abundance (LMA) sponge Callyspongia siphonella to 30.5 AE 10.5 μmol O 2 L À1 for the high microbial abundance HMA) sponge Theonella swinhoei with considerable variation in oxygen removal across all scales (minutes to hours, within and among specimens). Events of high oxygen removal (> 50 μmol L À1 ) were regularly observed for five of the seven species and were predominantly nocturnal, occasionally lasting several hours. The high variability in oxygen removal stresses the need for long-term in-situ measurements of benthic suspension feeders metabolism.