Research projects

We work on a broad range of ecological topics and are always keen to open up new research lines and establish new collaborations within and across research traditions and institutions.

Much of our research focus on biotic and abiotic conditions that control community structures and patterns of biodiversity, for example human stressors, biogenic habitat formation, niche differentiation, and biological invasions. Below are examples of active research lines that fascinate us, with relevant publications from our lab.

Field work is a crucial component for much of our research

Biological invasions in aquatic ecosystems

Invasions by non-native species have changed biological communities and food webs on local, regional, and global scales. We study these invasions in aquatic ecosystems from Denmark to New Zealand, rocky shores to muddy estuaries. Our driving questions include: how abundant are invaders and how do abundance patterns change in space and time? What are the ecological impacts of invaders? What makes some communities more susceptible to invasion than others? Do invaders have superior traits compared to native species?

We’re using simple frameworks to identify generalities that will let us better understand and predict the direction and magnitude of ecological impacts on native species abundances and community structures (reference ^1,2-35).

The invasive snail Batillaria australis provide substrate to native seaweeds (here Gracilaria comosa) in Swan river, Perth — The invasive snail Batillaria australis provides substrate to native seaweeds (here Gracilaria comosa) in Swan river, Perth

Habitat cascades

We study habitat cascades; a common type of a facilitation cascade where “indirect positive effects on focal organisms are mediated by successive formation or modification of biogenic habitat”. A habitat cascade is composed of at least three organisms: a primary habitat former or modifier; a secondary habitat former or modifier; and a focal organism that utilizes the secondary habitat former or modifier. For example, primary habitat forming trees can provide habitat for secondary habitat forming epiphytes, lianas, or vines that again can provide habitat to focal organisms like insects and birds. Habitat cascades promote increased biodiversity in ecosystems dominated by large and long-lived sessile or slow-moving structural organisms. For example, habitat cascades have been documented in tropical forests, temperate forests, salt marshes, coral reefs, seagrass beds, mangrove stands, polychaete gardens, seaweed covered rocky coasts and mollusc reefs. Our research focus mainly on processes that control the strength of habitat cascades from rocky intertidal and estuarine ecosystems.

A long habitat cascade in Avon Heathcote estuary, Austrovenus (bivalve) provide habitat to Gracilaria (red seaweed) that provide habitat to Ulva (green Seaweed) that provide habitat to Micrelenchus (snail) that provide habitat to Gigartina (red seaweed).... — A long habitat cascade in Avon Heathcote estuary: A partly buried Austrovenus (bivalve, left) provide habitat to Gracilaria (red seaweed) that provide habitat to Ulva (green Seaweed) that provide habitat to Micrelenchus (snail) that provide habitat to Gigartina (red seaweed, rigth)….

Impact of climate change and marine heatwaves on kelp forests

Coastal habitats are dynamic ecosystems, but human stressors can overwhelm natural variation by orders of magnitude, often to a point where local species cannot adapt or move. We want to understand the myriad impacts of climate change, including local community adaptation to increasing sea temperatures, and the synergistic impact of temperature and co-occuring stressors. Specifically, we’ve examined the interactions between temperature stress, invaders, and drifting seaweeds, and studied how temperature regimes impact the distribution, resilience, and ecological performance of habitat-forming organisms, invertebrates, and fish (reference ^{17,20,27,29,36-44}).

Laboratory experiment testing for interaction effects between elevated temperatures, invasive snails and drifting seaweeds on seagrass performance — Laboratory experiment testing for interaction effects between elevated temperatures, invasive snails, and drifting seaweeds on seagrass performance

Seagrasses as ecosystem stress indicators

Seagrasses provide habitat, food and shelter for a variety of plant and animals. They also act as sinks for land-derived pollutants and nutrients, and shelter coastlines by dampening waves and binding sediments. However, seagrass beds face a variety of threats, including invasive species, bloom-forming seaweeds, nutrient pollution, climate change, and coastal developments. The function of seagrass beds provides time-integrated indicators of environmental water quality. We study a broad range of questions related to seagrass ecology, conservation, restoration, and response to pertinent human stressors (reference ^{22,25,27-29,36,45,46}).

Seaweeds (here Ulva) often accumulate in seagrass beds (here Zostera muelleri), providing additional food and habitat for invertebrates but also competing for light and nutrients with the seagrass — Seaweeds (here, Ulva sp.) often accumulate in seagrass beds (here, Zostera muelleri), providing additional food and habitat for invertebrates, but also competing for light and nutrients with the seagrass

Facilitation: the importance of positive species interactions

Facilitation processes occur through direct positive interactions (mutualism, commensalism, biogenic habitat formation) and indirectly through cascading positive (cascading habitat-formation, facilitation cascades) and negative interactions (trophic cascades, keystone predation). Facilitation processes are increasingly included in ecological theory, and are an important aspect of coastal ecosystem conservation and management. We want to understand the impacts of facilitation in coastal ecosystems. For example: how do invertebrates create habitat for plants, and vice versa? What are the cascading implications on community structures and ecosystem properties (reference ^{4,21,27,39-41,46,47,48-51})

Cockle shells provide attachment space for estuarine seaweeds — Cockle shells facilitate estuarine seaweeds by providing an attachment substrate

Co-existence of ‘rare’ species

The scientific literature is dominated by research about conspicuous, iconic and abundant species. However, it is the rarer, subdominant, and inconspicuous species that make up the bulk of the world’s biodiversity. It is these rarer species that are most vulnerable to extinctions following human disturbances and stressors and therefore need to be cataloged and their ecologies understood. We study a broad range of questions about processes that promotes or inhibit rarer subdominant species, such as disturbances, anthropogenic stressors, facilitation processes, and habitat filtering (reference ^{2,3-5,8,9,12,13})

Survey of 'rare' Caulerpa seaweeds in Western Australia — Survey of ‘rare’ Caulerpa seaweeds in Western Australia

Reef ecology

Coastal reefs are topographic complex structures embedded in a simpler matrix, such as oyster reef surrounded by mud or limestone reefs surrounded by sand. Reefs are areas of high productivity and biodiversity, that ‘spill-over’ excess energy and matter to adjacent habitats. Reefs vary in sizes from 1000’s of km² (Great Barrier Reef) to a few m² (e.g. oyster reefs). There are no fixed spatial limits for what constitute a reef, and individual stones, shells and polychaete tubes, have many of the properties associated with larger reef structures, that is micro-reefs” are typically also more diverse than the adjacent matrix. We study different types and reef sizes to develop general models to better understand how diversity hotspots are generated and maintained (reference ^{2,8,10,13,22,27,28,40-44,46,48,49,52-54}).

Surveys and experiments are conducted on intertidal reefs on the south island of New Zealand

Success and impact of estuarine seaweeds

Unattached seaweeds that drift around with tidal currents, and seaweeds attached to scattered hard substrates are natural features of sedimentary estuaries. These estuarine seaweeds provide food for birds, fish and invertebrates, habitat for flora and fauna, and can connect and transfer organisms and energy between different estuarine habitats, such as oyster refs, mudflats, salt marshes and seagrass beds. However, estuarine seaweeds can also proliferate into massive blooms particular under nutrient rich conditions. These blooms can cause similar ecological and problems as do many invasive species and terrestrial weeds. We study a broad range of questions in relation to what drive the success of estuarine seaweeds and their ecological impacts on oyster reefs, seagrass beds, sedimentary infauna and salt marshes (reference ^{1,2-5,8,9,12-14,21,22,24,27,29,36,45,47,48,55-57}).

Accumulations of large seaweed mats, fuelled by nutrient pollution, can have detrimental effects on fauna living in the sediment and seagrasses

Habitat linkages

Habitats and ecosystems do not exist in isolation. Rather, habitats are open systems that are connected via flow of matter (e.g., organisms) and energy. For example, an oyster reef may be unable to persist if the reef is constantly smothered by drifting seaweeds that is transported from nearby seaweed meadows. To understand the ecology of a specific habitat therefore requires additional insight into the ecology of its surrounding habitats. We study a broad range of question related to habitat-linkages and spatial subsidies in coastal systems, for example between oyster reefs and mudflats, mudflats and salt marshes, and kelp forests and seagrass beds (reference ^{8,21,39,40,46,53}.).

Seaweed is produced in polychaete gardens (left) but, during storms, dislodged and transported to adjacent saltmarshes (right) where new invertebrates colonize this novel habitat — Seaweeds mats (the invasive Gracilaria vermiculophylla) are produced in polychaete gardens (left) but dislodges during storms, and are transported to adjacent saltmarshes (right) where new invertebrate communities colonize this novel habitat.

Marine macroecology; linking ecology and biogeography

Ecologists have traditionally studied the factors that influence the distribution and abundance of organisms on small and short scales, whereas biogeographers have addressed similar questions on larger and longer scales. However, there is no single fixed scale to study organisms and processes, and it increasingly recognized that the methods and scientific insights from these two research traditions should be supplementary, rather than competing. Most of our research has been conducted on the ecological scales, but we are also interested in biogeographical patterns of distribution of marine plants and animals, have used phylogenetics to disentangle evolutionary histories, have conducted comparative experiments along 100’s of km coastline, and compared key ecological processes across biogeographical regions (reference ^{14,16,17,23,27,38-40,42,49,58}).

Macro-ecological patterns in phase shift from kelp forests to seaweed turfs following a heat wave in 2011 in Western Australia changing from dense Kelp forests (Ecklonia radiata) to seaweed turf (B). The map show the extent of kelp forests, with colors showing the proportion lost. The bars show the actual kelp forest areas, with an average of 40% loss (initially covering ca. 2,300 km2). — Macro-ecological patterns in phase shift from kelp forests to seaweed turfs following a heat wave in 2011 in Western Australia changing from dense Kelp forests (*Ecklonia radiata*) to seaweed turf (B). The map show the extent of kelp forests, with colors showing the proportion lost. The bars show the actual kelp forest areas, with an average of 40% loss (initially covering ca. 2,300 km2).

Kelp bed ecology

Kelp beds are productive plant communities that dominate wave-exposed reefs and rocky coasts from polar to warm-temperate latitudes. Kelp beds provide habitat, food and shelter for a variety of marine plant and animals and shelter coastlines by dampening waves. However, kelp beds are threatened by invaders and nuisance species, nutrient pollution, climate changes and coastal developments. We study a range of questions in relation to kelp ecology and their most pertinent human stressors, for example impact of global warming, the ecological importance of morphological variability and biomechanical properties of kelps, linkages to adjacent habitats, and the importance of kelp beds as habitat for seaweeds, invertebrates, and fishes (reference ^{38-42,46,49,52,53-55,59}).

Measuring attachment strength of the kelp Ecklonia radiata in Western Australia

Human impacts on salt marshes

Coastal salt marshes provide habitat, food and shelter for a variety of marine and terrestrial plant and animals. Salt marshes are also sinks for land-derived pollutants and nutrients and shelter coastlines by dampening waves and binding sediments. However, many salt marshes are threatened by invaders and nuisance species, climate changes and coastal developments. Impacts of anthropogenic stressors on intertidal salt marshes have long been investigated in North America and Europe. In comparison, less is known about impacts in Australasian salt marshes. We use manipulative experiments and surveys to test if anthropogenic stressors, for example nutrient enrichment and invasive species, affect species distribution and zonation patterns in Australasian salt marshes (reference ^20,21,37).

The invasive seaweed Gracilaria vermiculophylla have invaded salt marshes along the the US east coast, altering community structures and nutrient fluxes

Relevant Lab-publications

1 Wernberg, T., Thomsen, M. S. & Stæhr, P. A. Invasion af butblærret Sargassotang i Danmark – status anno 1998. Urt 4, 128-134 (1998).

2 Staehr, P. A., Pedersen, M. F., Thomsen, M. S., Wernberg, T. & Krause-Jensen, D. Invasion of Sargassum muticum in Limfjorden (Denmark) and its possible impact on the indigenous macroalgal community. Marine Ecology Progress Series 207, 79-88 (2000).

3 Wernberg, T., Thomsen, M. S., Stæhr, P. A. & Pedersen, M. F. Comparative phenology of Sargassum muticum and Halidrys siliquosa (Phaeophyceae: Fucales) in Limfjorden, Denmark. Botanica Marina 44, 31-39, doi:10.1515/BOT.2001.005 (2001).

4 Wernberg, T., Thomsen, M. S., Staerh, P. A. & Pedersen, M. F. Epibiota communities of the introduced and indigenous macroalgal relatives Sargassum muticum and Halidrys siliquosa in Limfjorden (Denmark). Helgoland Marine Research 58, 154-161 (2004).

5 Pedersen, M. F., Stæhr, P. A., Wernberg, T. & Thomsen, M. Biomass dynamics of exotic Sargassum muticum and native Halidrys siliquosa in Limfjorden, Denmark – implications of species replacements on turnover rates. Aquatic Botany 83, 31–47 (2005).

6 Thomsen, M. S., Krause-Jensen, D., Wernberg, T., Staerh, P. A. & Risgaard-Petersen, N. Fremmede tangarter i Danmark: Hvilke? Hvor udbredte? Hvornaar? Urt 29, 110-115 (2005).

7 Thomsen, M. S., Gurgel, C. F. D., Fredericq, S. & McGlathery, K. J. Gracilaria vermiculophylla (Rhodophyta, Gracilariales) in Hog Island Bay, Virginia: a cryptic alien and invasive macroalgae and taxonomic corrections. Journal of Phycology 42, 139-141 (2006).

8 Thomsen, M. S. & McGlathery, K. Effects of accumulations of sediments and drift algae on recruitment of sessile organisms associated with oyster reefs. Journal of Experimental Marine Biology and Ecology 328, 22-34 (2006).

9 Thomsen, M. S., McGlathery, K. & Tyler, A. C. Macroalgal distribution pattern in a shallow, soft-bottom lagoon, with emphasis on the nonnative Gracilaria vermiculophylla and Codium fragile. Estuaries and Coasts 29, 470–478 (2006).

10 Thomsen, M. S., Wernberg, T., Stæhr, P. A. & Pedersen, M. F. Spatio-temporal distribution patterns of the invasive macroalga Sargassum muticum within a Danish Sargassum-bed. Helgoland Marine Research 60, 50-58 (2006).

11 Thomsen, M. S., Josefson, A. & Wernberg, T. Hvor almindelige er bundlevende indførte marine invertebrater i Danmark? Vand og Jord 2, 44-48 (2007).

12 Thomsen, M. S. & McGlathery, K. J. Stress tolerance of the invasive macroalgae Codium fragile and Gracilaria vermiculophylla in a soft-bottom turbid lagoon. Biological Invasions 9, 499-513 (2007).

13 Thomsen, M. S., Silliman, B. R. & McGlathery, K. J. Spatial variation in recruitment of native and invasive sessile species onto oyster reefs in a temperate soft-bottom lagoon. Estuarine, Coastal and Shelf Science 72, 89-101 (2007).

14 Thomsen, M. S. et al. Gracilaria vermiculophylla in northern Europe, with focus on Denmark, and what to expect in the future. Aquatic Invasions 2, 83-94 (2007).

15 Thomsen, M. S., Staehr, P. A. & Wernberg, T. First Symposium on Danish Marine Bioinvasions, Copenhagen August 17: A PDF abstract booklet, with introduction and summery. Symposium Abstract Book, 18 (2007).

16 Thomsen, M. S. et al. Alien macroalgae in Denmark – a national perspective. Marine Biology Research 3, 61-72 (2007).

17 Thomsen, M. S. et al. Status and trends of non-indigenous macro-benthic marine species in Denmark. Aquatic Invasions 3, 133-139 (2008).

18 Thomsen, M. S. et al. Introducerede dyr og planter i Danmark – terminologi, mekanismer og effekter. Naturens Verden 6, 10-18 (2008).

19 Nyberg, C. D., Thomsen, M. S. & Wallentinus, I. Flora and fauna associated with the introduced red alga Gracilaria vermiculophylla. European Journal of Phycology 44, 395 – 403 (2009).

20 Thomsen, M. S., Adam, P. & Silliman, B. Anthropogenic threats to Australasian coastal salt marshes. In Anthropogenic Modification of North American Salt Marshes (ed. B.R. Silliman, M.D. Bertness, D. Strong), University of California Press., 361-390 (2009).

21 Thomsen, M. S., McGlathery, K. J., Schwarzschild, A. & Silliman, B. R. Distribution and ecological role of the non-native macroalga Gracilaria vermiculophylla in Virginia salt marshes. Biological Invasions 11, 2303-2316, doi:10.1007/s10530-008-9417-9 (2009).

22 Thomsen, M. S. & Wernberg, T. Distribution, abundance and linkages between drift algae and an invasive snail in seagrass beds in Swan River, Western Australia. Report no. CMER-2009-02 from the Centre for Marine Ecosystem Management, Edith Cowan University, Perth, prepared for the Swan River Trust, 50 (2009).

23 Thomsen, M. S., Wernberg, T., Silliman, B. & Josefson, A. Broad-scale patterns of abundance of non-indigenous soft-bottom invertebrates in Denmark. Helgoland Marine Research 63, 159-167 (2009).

24 Thomsen, M. S., Wernberg, T., Tuya, F. & Silliman, B. R. Evidence for impacts of non-indigenous macroalgae: a meta-analysis of experimental field studies. Journal of Phycology 45, 812-819 (2009).

25 Thomsen, M. S. Experimental evidence for positive effects of invasive seaweed on native invertebrates via habitat-formation in a seagrass bed. Aquatic Invasions 5, 341–346 (2010).

26 Thomsen, M. S. & Staehr, P. A. Second Symposium on Danish Marine Bioinvasions, Copenhagen September 3: A PDF abstract booklet, with introduction. Symposium Abstract Book, 16 (2010).

27 Thomsen, M. S. et al. Habitat cascades: the conceptual context and global relevance of facilitation cascades via habitat formation and modification. Integrative and Comparative Biology 50, 158-175 (2010).

28 Thomsen, M. S., Wernberg, T., Tyua, F. & Silliman, B. Ecological performance and possible origin of a ubiquitous but under-studied gastropod. Estuarine, Coastal and Shelf Science 87, 501-650 (2010).

29 Hoeffle, H., Thomsen, M. S. & Holmer, M. Effects of the invasive macroalgae Gracilaria vermiculophylla on the seagrass Zostera marina under different temperature regimes. Estuarine, Coastal and Shelf Science (2011).

30 Thomsen, M. S., Wernberg, T., Olden, J. D., Griffin, J. N. & Silliman, B. R. A framework to study the context-dependent impacts of marine invasions Journal of Experimental Marine Biology and Ecology (2011).

31 Thyrring, J., Thomsen, M. S., Brunbjerg, A. K. & Wernberg, T. Diversity and abundance of epibiota on invasive and native estuarine gastropods depend on substratum and salinity. Marine and Freshwater Research 66, 1191–1200 (2015).

32 Thomsen, M. S., Wernberg, T. & Schiel, D. R. in Marine ecosystems: human impacts on biodiversity, functioning and services (eds T. P. Crowe & C. L. J. Frid) 274-332 (Cambridge University Press, 2015).

33 Tait, L. W., South, P. M., Lilley, S. A., Thomsen, M. S. & Schiel, D. R. Assemblage and understory carbon production of native and invasive canopy-forming macroalgae. Journal of Experimental Marine Biology and Ecology 469, 10-17, doi:http://dx.doi.org/10.1016/j.jembe.2015.04.007 (2015).

34 Thomsen, M. S. et al. Forty years of experiments on invasive species: are biases limiting our understanding of impacts? . Neobiota 22, 1-22 (2014).

35 Thomsen, M. S. et al. Impacts of marine invaders on biodiversity depend on trophic position and functional similarity. Marine Ecology Progress Series 495, 39-47 (2014).

36 Holmer, M., Wirachwong, P. & Thomsen, M. S. Negative effects of stress-resistant drift algae and high temperature on a small ephemeral seagrass species. Marine Biology (2011).

37 Silliman, B. R., Bertness, M. & Thomsen, M. S. Trophic cascades and climate change in southern US marshes: Will the over-harvesting of blue crabs and drought stress trigger massive die-off of southern salt marshes? In Anthropogenic Modification of North American Salt Marshes (ed. B.R. Silliman, M.D. Bertness, D. Strong), University of California Press., 103-114 (2009).

38 Tuya, F., Wernberg, T. & Thomsen, M. S. Testing the ‘abundant centre’ hypothesis on endemic reef fishes in south-western Australia. Marine Ecology Progress Series 372, 225–230 (2008).

39 Tuya, F., Wernberg, T. & Thomsen, M. S. Colonization of gastropods on subtidal reefs depends on density in adjacent habitats, not on disturbance regime. Journal of Molluscan Studies 75, 27–33 (2009).

40 Tuya, F., Wernberg, T. & Thomsen, M. S. Habitat structure affect abundances of labrid fishes across temperate reefs in south-western Australia. Environmental Biology of Fishes 86, 311–319 (2009).

41 Wernberg, T., Thomsen, M. S., Tuya, F. & Kendrick, G. Biogenic habitat structure on reefs change along a latitudinal gradient in temperate ocean climate. Journal of Experimental Marine Biology and Ecology (2011).

42 Wernberg, T. et al. The resilience of Australasian kelp beds decrease along a latitudinal gradient in ocean temperature. Ecology Letters 13, 685–694 (2010).

43 Wernberg, T. et al. Climate driven regime shift of a temperate marine ecosystem. Science 353, 169-172 (2016).

44 Wernberg, T. et al. An extreme climatic event alters marine ecosystem structure in a global biodiversity hotspot. Nature Clim. Change 3, 78-82, doi:http://www.nature.com/nclimate/journal/v3/n1/abs/nclimate1627.html#supplementary-information (2013).

45 Wernberg, T., Thomsen, M. S. & McMahon, K. Determining seagrass depth distribution in the Swan River – a test of the dumpy level method with recommendations for alternatives. Report no. CMER-2008-02 from the Centre for Marine Ecosystems Research, Edith Cowan University, Perth, prepared for the Water Science Branch, Department of Water., 18 (2008).

46 Tuya, F. et al. Proximity to edges impacts cross-habitat flows: implications for abundance patterns and species interactions. Marine Ecology Progress Series 405, 175–186 (2010).

47 Thomsen, M. S. Species, thallus size and substrate determine macroalgal break forces and break places in a low-energy soft-bottom lagoon. Aquatic Botany 80, 153-161 (2004).

48 Thomsen, M. S. & McGlathery, K. Facilitation of macroalgae by the sedimentary tube forming polychaete Diopatra cuprea. Estuarine, Coastal and Shelf Science 62, 63-73 (2005).

49 Wernberg, T., Tuya, F., Thomsen, M. S. & Kendrick, G. A. Turban snails as habitat for foliose algae: contrasting geographical patterns in species richness explained by top-down control from limpets? Marine and Freshwater Research 61, 1-6 (2010).

50 Thomsen, M. S., Metcalfe, I., South, P. & Schiel, D. R. A host-specific habitat former controls biodiversity across ecological transitions in a rocky intertidal facilitation cascade. Marine and Freshwater Research 67, 144-152 (2016).

51 Thomsen, M. S. & Wernberg, T. On the generality of cascading habitat-formation. Proceedings of the Royal Society B: Biological Sciences 281(1777):20131994 (2014).

52 Thomsen, M. S. & Wernberg, T. What affects the forces required to break or dislodge macroalgae? A minireview. European Journal of Phycology 40, 1-10 (2005).

53 Tuya, F., Wernberg, T. & Thomsen, M. S. The spatial arrangement of reefs alters the ecological patterns of fauna between interspersed algal habitats. Estuarine, Coastal and Shelf Science 78, 774-782 (2008).

54 Wernberg, T. & Thomsen, M. S. The effect of wave exposure on the morphology of Ecklonia radiata in southwestern Australia. Aquatic Botany 83, 61–70 (2005).

55 Thomsen, M. S., Wernberg, T. & Kendrick, G. A. The effect of thallus size, life stage, aggregation, wave exposure and substrate conditions on the forces required to break or dislodge the small kelp Ecklonia radiata. Botanica Marina 47, 454-460, doi:10.1515/BOT.2004.068 (2004).

56 Ramsey, E., Rangoonwala, A., Thomsen, M. S. & Schwarzschild, A. Spectral definition of the macro-algae Ulva curvata in the back-barrier bays of the Eastern Shore of Virginia, USA. International Journal of Remote Sensing (2011).

57 Thomsen, M. S. & Wernberg, T. The devil in the detail: harmful seaweeds are not harmful to everyone. Global Change Biology 21, 1381-1382 (2015).

58 Waters, J. M. et al. Australia’s marine biogeography revisited: back to the future? Austral Ecology 35, 988–992 (2010).

59 Wernberg, T., Coleman, M., Fairhead, A., Miller, S. & Thomsen, M. S. Morphology of Ecklonia radiata (C. Ag.) J. Agardh. along its geographic distribution in Southwestern Australia and Australasia. Marine Biology 143, 47-55, doi:10.1007/s00227-003-1069-9 (2003).