The invasive red alga Gracilaria vermiculophylla in the Baltic Sea: adaptation to brackish water may compensate for light limitation

Abstract

The recent introduction of Gracilaria vermiculophylla (Rhodophyta) to the Kiel Fjord area was a reason for concern, since this red macroalga perfoms best under mesohaline conditions and thus appears well adapted to thrive and spread in the Baltic Sea environment. A systematic survey on a coastal range of 500 km in 2006 and 2007 indicated considerable multiplication and spreading of G. vermiculophylla within Kiel Fjord, but provided little evidence of long-distance transport. Nonetheless, flow-through growth experiments conducted at a range of salinities under ambient light showed that G. vermiculophylla should be able to grow in most of the Baltic Sea. Growth declined only below a salinity of 5.5. High water temperatures in summer seem to reduce resistance against low salinity. Growth of G. vermiculophylla in the SW Baltic is limited by light and is only possible during summer and above a depth of 3 m. Drifting fragments are dispersed by currents. Either they sink to deeper waters, where they degrade, or they accumulate in shallow and sheltered waters, where they form perennial mats. These overgrow not only soft bottom sediments, but also stones, which are an important habitat to Fucus vesiculosus, the main native perennial alga in the Baltic Sea. As compared to F. vesiculosus, G. vermiculophylla seems to represent a preferred refuge for mesograzers and other invertebrates, particularly in winter. Nonetheless, feeding trials showed that potential grazers avoided G. vermiculophylla relative to F. vesiculosus. Daily biomass uptake by grazers associated with G. vermiculophylla in nature did not exceed 2 g kg -1 and is <11% of average daily net growth (18.5 g kg -1 ) in the first 2 m below sea level. Consequently, feeding may not be sufficient to control the spread of G. vermiculophylla in the SW Baltic. Our study suggests that absence of feeding enemies and adaptation to brackish water may allow G. vermiculophylla to invade most shallow coastal waters of the inner Baltic Sea despite light limitation.

Temperature- and light-dependent growth and metabolism of the invasive red algaeGracilaria vermiculophylla– a comparison with two native macroalgae

“…Our findings suggest that G. vermiculophylla should generally be able to sustain positive growth in shallow Scandinavian estuaries during all seasons (except for the low saline parts (<5 PSU) of the Baltic Sea). This is in contrast to the findings of Weinberger et al (2008) who performed in situ experiments and found positive growth rates in G. vermiculophylla during the summer (high temperature and high light) but not during spring and autumn, when there was reduced light and temperature. However, biomass loss caused by mesoherbivores and fragmentation (potentially induced by the grazers) in the field experiment may explain this discrepancy.…”

“…However, biomass loss caused by mesoherbivores and fragmentation (potentially induced by the grazers) in the field experiment may explain this discrepancy. Indeed, Weinberger et al (2008) recorded higher grazing rates than were reported by Nejrup & Pedersen (2010). Low temperatures and ice cover (i.e.…”

“…In the E Atlantic, G. vermiculophylla was first observed along the French coastline (Mollet et al, 1998;Rueness, 2005). Following the first sighting in Europe, it has subsequently been found south of France, in Spain, Portugal, Italy and Morocco (Kim et al, 2010;Sfriso et al, 2010); and also northwards, in the North Sea and Wadden Sea, and penetrating into the Baltic Sea, where it is now present on the west coast of Sweden (Nyberg, 2006;Nyberg et al, 2009), in many of the Danish fjords in the Baltic area (Thomsen et al, , 2008, and in the bay of Kiel (Weinberger et al, 2008).…”

“…Growth in Scandinavian G. vermiculophylla populations has only been measured in field experiments. However, field experiments are characterized by uncontrolled co-varying factors such as day length, grazing rates and nutrient levels, making it difficult to identify temperature and light responses (Weinberger et al, 2008;Nejrup & Pedersen, 2010). To understand the mechanisms that control growth of G. vermiculophylla in the Baltic region and to be able to generate quantitative and predictive performance models, controlled laboratory experiments that focus on the effects of light and temperature, and also potential interactive effects, are required.…”

Effects of limitation stress and of disruptive stress on induced antigrazing defense in the bladder wrack Fucus vesiculosus

“…The proposed scenario corresponds with the fact that Idotea baltica is virtually absent from Fucus vesiculosus in the German Baltic Sea and in winter, but not from other algae in the close vicinity of F. vesiculosus (Weinberger et al 2008). Since the presence of I. baltica alone is not sufficient to induce antifeeding defense, consumption is required (Rohde et al 2004) and an absence of consumption due to low palatability at low light conditions should result in no triggering of defense.…”