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 substratum
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 during
the settlement seasons of 2003 to 2005. The forcing factors were wind direction, predicted residual
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 pattern.
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 transport
processes and local movement of larvae in C. maenas and other invertebrates with mobile benthic
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 understand
the temporal and spatial patterns of organism
abundance. In marine benthic species, a better understanding
of such patterns is achieved if studies integrate
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 processes/factors
usually affect benthic organisms at different
spatial scales. Benthic processes, e.g. interactions
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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