í*h\ Vs'9-tr 
Vol. 338:159-168,2007 
MARINE ECOLOGY PROGRESS SERIES 
Mar Ecol Prog Ser 
Published May 24 
Settlement of shore crab Carcinus maenas 
on a mesotidal open habitat as a function 
of transport mechanisms 
Luis Giménez 1,2 *, Stephan Dick 3 
'Biologische Anstalt Helgoland, Foundation Allred Wegener Institute for Polar and Marine Research, 27498 Helgoland, Germany 
2 Sección Oceanología, Facultad de Ciencias, Iguá 4225, 11400 Montevideo, Uruguay 
Bundesamt für Seeschifffahrt und Hydrographie, Bernhard-Nocht-StraBe 78, 20359 Hamburg, Germany 
ABSTRACT: We evaluated the patterns of larval settlement of Carcinus maenas on natural substra 
tum and its relationships with forcing factors related to larval transport mechanisms. Settlement was 
estimated as colonisation of traps containing defaunated substratum. Traps were deployed at low tide 
for 24 to 26 h, in the intertidal of the island of Helgoland (North Sea, German Bight), every day dur 
ing the settlement seasons of 2003 to 2005. The forcing factors were wind direction, predicted resid 
ual surface (0 to 8 m) currents, and days since spring tide. The settlement season lasted from the end 
of June to the end of August; colonisation rates varied among and within years, without a clear pat 
tern. In 2003 and 2004, long periods of low colonisation rates occurred in association with strong and 
persistent (5 to 10 d) SW winds and eastward currents. In 2003, colonisation peaked at spring tide 
only when winds were not from SW and currents were not flowing eastwards. In 2005, colonisation 
rates peaked mainly at, or 1 to 3 d after, spring tide; periods of low colonisation were short, except at 
the end of the settlement season. According to an existing 2-step model and to local movement of 
megalopae, colonisation patterns in the intertidal may reflect transport processes: (1) settlement rates 
on Helgoland are primarily affected by wind-driven currents: SW winds transport larvae out of 
Helgoland waters, leading to low settlement rates, while other wind regimes transport them towards 
Helgoland. In the absence of strong SW winds, peaks of settlement at or after spring tide suggest 
(2) selective tidal stream transport or some form of tidally mediated flow. The absence of SW winds 
leads to a higher influence of local movement of megalopae, as the number of larvae reaching the 
benthic habitat is high. In consequence, colonisation of natural substratum may reflect larval trans 
port processes and local movement of larvae in C. maenas and other invertebrates with mobile ben 
thic stages. 
KEY WORDS; Settlement • Recruitment ■ Megalopae ■ Larval transport ■ Postsettlement movements ■ 
North Sea 
Resale or republicstion not permitted without written consent of the publisher 
INTRODUCTION 
One of the central objectives of ecology is to under 
stand the temporal and spatial patterns of organism 
abundance. In marine benthic species, a better under 
standing of such patterns is achieved if studies inte 
grate different phases of their life cycles (Bhaud 1998, 
Connolly & Roughgarden 2003, Giménez 2004). 
Email; luis.gimenez@awi.de 
Present address: Montevideo 
BSH-Bibliothek 
0889947 
In sessile benthic species, benthic and pelagic pro 
cesses/factors usually affect benthic organisms at dif 
ferent spatial scales. Benthic processes, e.g. interac 
tions between larvae and resident species (Osman et 
al. 1989, Jenkins et al. 1999) or benthic predation and 
competition among juveniles/adults, occur at spatial 
scales of metres (Roughgarden et al. 1988). Pelagic 
processes, such as those influet 
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