Effects of boat traffic and mooring infrastructure on aquatic vegetation: A systematic review and meta-analysis.

Sustainable management of coastal and inland water areas requires knowledge of how tourism and recreation affects the ecosystems. Here, we present the first systematic review and meta-analysis to quantify to what extent recreational boat traffic and infrastructure for mooring affect the abundance of submerged vegetation on soft bottoms. Our systematic search yielded 25 studies containing data on effects of boat traffic, docks and mooring buoys on vegetation abundance. The abundance below docks was on average 18% of that in controls, and areas with boat traffic had on average 42% of the abundance in control areas. Mooring buoys often created scour areas without vegetation. However, the effects were variable and there were too few studies to test the reasons for this variability. We conclude that boating can cause significant declines in submerged vegetation but that informed management of boat traffic and improved design of docks and buoys can reduce negative impacts.

Divergent ecological strategies determine different impacts on community production by two successful non-native seaweeds.

The consequences of plant introductions into ecosystems are frequently reported from terrestrial environments, but little is known about the effects on ecosystem functioning caused by non-native primary producers in marine systems. In this study we explored the effects of the invasion by the two filamentous red algae Heterosiphonia japonica and Bonnemaisonia hamifera on the primary production of seaweed communities by using single and mixed cultures of non-native and native red algae. The experiments were conducted both in the presence and absence of herbivores. Biomass production of the invaded community increased more than four times in mixed cultures with H. japonica, while introduction by B. hamifera had no significant effect. The different impact on community production could be explained by differences in life history strategies between the invaders; H. japonica grew considerably faster than the native seaweeds which directly increased the community production, while B. hamifera showed a relatively slow growth rate and therefore had no effect. From previous studies it is known that B. hamifera produces a highly deterrent, but also costly, chemical defence. The assessment of survival and growth of a native generalist herbivore further corroborated that the biomass produced by B. hamifera constitutes a very low-quality food, whereas the performance of herbivores on a diet of H. japonica was comparable to that on native algal diets. In summary, this study demonstrates that successful invaders belonging to the same functional group (filamentous red algae) may have distinctly different impacts on productivity in the recipient community, depending on their specific life history traits.