<i>Lanice conchilega</i>, fisheries and marine conservation: Towards an ecosystem approach to marine management

This doctoral thesis bridges experimental research and policy issues in the marine environment. The focus is on the challenging relation between nature conservation and current fisheries practices. The study sites investigated consist largely of sedimentary sand banks and swales, situated in North-Western Europe. A particular biogenic habitat has been chosen to study both the ecological importance and the resilience towards the physical disturbance of beam-trawling. This habitat is Lanice conchilega reefs, which are distinct aggregations of tube dwelling polychaetes (bristle worms). The implications of these tube worm reefs for the benthic environment as well as for flatfish species are studied in depth and several experiments (in lab and field conditions) quantify the impact of beam trawl fisheries. The thesis finishes by integrating these results in legal policy options and discusses the process of MPA-implementation. The general discussion elaborates how this thesis may contribute to the application of an ecosystem approach to support marine managemen

The resistance of <i>Lanice conchilega</i> reefs to physical disturbance

One way to generate detailed knowledge of the response to physical disturbance is quantifying the resistance of biogenically created emergent structures towards fisheries. The biogenic structures targeted in the present study are shaped by the ecosystem engineering polychaeteLanice conchilega. Direct mortality ofL. conchilega as a consequence of sustained physical disturbance at varying frequencies has been tested to quantify the resilience of this particular reef system. Research is based on a laboratory experiment in which four different disturbance regimes were applied (disturbance every other 12, 24 and 48 h and no fishing disturbance as a control). Survival proportions were measured over time and tested with a generalized linear mixed model (GLMM). Survival dropped ignificantly after 10 and 18 days (with a disturbance frequency of every 12 and 24 h, respectively). The results indicate that L.conchilega is relatively resistant to physical disturbance but that reef systems can potentially collapse under continuous high frequency disturbance. The results of this experiment are discussed in the light of beam trawl fisheries, a common physical disturbance in areas where knowledge of the general resilience

<i>Lanice conchilega</i>, fisheries and marine conservation: Towards an ecosystem approach to marine management

This doctoral thesis bridges experimental research and policy issues in the marine environment. The focus is on the challenging relation between nature conservation and current fisheries practices. The study sites investigated consist largely of sedimentary sand banks and swales, situated in North-Western Europe. A particular biogenic habitat has been chosen to study both the ecological importance and the resilience towards the physical disturbance of beam-trawling. This habitat is Lanice conchilega reefs, which are distinct aggregations of tube dwelling polychaetes (bristle worms). The implications of these tube worm reefs for the benthic environment as well as for flatfish species are studied in depth and several experiments (in lab and field conditions) quantify the impact of beam trawl fisheries. The thesis finishes by integrating these results in legal policy options and discusses the process of MPA-implementation. The general discussion elaborates how this thesis may contribute to the application of an ecosystem approach to support marine managemen

Biogenic reefs as structuring factor in <i>Pleuronectes platessa</i> (Plaice) nursery

The structural distribution of juvenile flatfish in nursery areas is generally studied on a larger scale on which the effects of abiotic factors such as sediment characteristics, beach profile, tides, and turbidity dominate. The biotic structuring factor has never before been investigated from a very small scale-perspective. The latter is the subject of the present study. In an in situ experimental sampling design, the structuring effect of biogenic reefs on the distribution of Pleuronectes platessa (Plaice) in an intertidal nursery area is investigated. The density distribution of this flatfish species is significantly (p Lanice conchilega. The importance of this reef builder has been highlighted before in other studies but present study demonstrates that not only the benthic biodiversity is affected by L. conchilega reefs, but that the distribution pattern of P. platessa is structured by them as well. This structuring impact of small-scale benthic reefs creating a patchy environment in nursery areas potentially plays an important role in other marine environments and indicates the need for further research on the ecological function of benthic reef environments for several flatfish species. Further modification of these biogenic habitats may lead to a loss of one or more ecosystem functions which flatfish species depend on

Experimental beam-trawling in <i>Lanice conchilega</i> reefs: impact on the associated fauna

To study fisheries impact at the species level in temperate sandy bottom areas, a controlled field manipulation experiment was designed focusing on areas with high densities of the habitat-structuring, tube-dwelling polychaete Lanice conchilega (i.e. L. conchilega reefs). The hypothesis was that the impact on L. conchilega would be minimal, but that the fauna benefiting from the biogenically structured habitat would be impacted by beam-trawling. In this study, the impact of beam-trawl passage on intertidal L. conchilega reefs and its associated fauna was quantified. A treatment zone was exposed to a one-off experimental trawling. Subsequently, the impact on and recovery of the associated fauna was investigated for a period of 9 days post-impact. Community analysis showed a clear impact followed by a relatively quick recovery as apparent through MDS analysis (stress 0.06), a significant (p p = 0.001) dissimilarities between treatment and control and through SIMPER analysis (decreasing dissimilarities over time). This impact and subsequent recovery was largely explained by two species: Eumida sanguinea and Urothoe poseidonis. Species analysis confirmed the beam-trawl passage significantly (p = 0.001) impacted E. sanguinea for the whole period of the experiment. The experiment confirmed that closely associated species of L. conchilega reefs are impacted by beam-trawl fisheries. This small-scale intertidal study provides some pointers which indicate that the tightly associated species will be impacted significantly when beam-trawling L. conchilega reefs in subtidal areas

A bio-engineered soft-bottom environment: the impact of <i>Lanice conchilega</i> on the benthic species-specific densities and community structure

This paper evaluates the effect of the tube-building, habitat structuring polychaete Lanice conchilega on the macrobenthic community and sediment characteristics of its habitat. To investigate which factors make species occur in a well-known bio-engineered habitat, macrofaunal and sedimentological data, gathered over a period of 10 years in a shallow, fine sediment bottom of the Belgian Part of the North Sea, were submitted to analyses. Both sediment composition and community structure of the associated macrofaunal matrix were affected by the presence of L. conchilega. The effect of the protruding tubes on hydrodynamics clearly resulted in the retention of fine sediment particles, while the increased coarse fraction was assumed to reflect a dynamic population build-up. This study confirmed that tube aggregations of L. conchilega expand the realized niche of several species without forming their own association. A species rank list was created according to each species’ association with L. conchilega. This species rank list is extensively discussed based on all ecological knowledge available. Species are favoured by the habitat modifying ability of the polychaete tubes, which create and regulate refuge for species, alter the interactions between local species and change the physical factors of the environment. This descriptive and correlative data study examines the ecological mportance of the bioengineer L. conchilega on species level

Importance of eco-engineered inshore habitats for juvenile flatfish

Within coastal nurseries, the distribution of juvenile flatfish may depend on small-scale habitat variability. The present study investigates the relation between the distribution of two juvenile flatfish species (Pleuronectes platessa and Limanda limanda) with two sessile tube dwelling polychaetes that create specific habitats at high densities. Their modulating effects make them classify as ecosystem engineers. Lanice conchilega and Owenia fusiformis, both frequently occurring in the coastal zones of the North Sea are the studied ecosystem engineers. These two benthic tube worm systems are investigated for their function as ‘essential juvenile habitat’ (EJH) in two geographical areas (the Belgian part of North Sea and the Dutch part of the Wadden Sea). General responses were identified by comparing relative differences between ecosystem engineered habitats and adjacent bare sand (i.e. non ecosystem engineered) habitats. Results show that both flatfish species select for the ecosystem engineered habitat. This behaviour was further investigated using stomach content analyses. For P. platessa occurring in L. conchilega habitat, this selection was explained as feeding behaviour. For the habitats created by O. fusiformis, no such a relation was found. For L. limanda higher densities within the ecosystem engineered habitats cannot be explained by feeding advantage but by the use of this habitat as a shelter. Therefore, higher flatfish densities could be explained by an antipredation behaviour. Lanice conchilega aggregations may be more important as feeding area for juvenile flatfish species in comparison with O. fusiformis aggregations. The indirect impacts of bottom trawling on benthic tube worm aggregations by reducing the suitability of the areas for juvenile flatfishes are discussed. We conclude that the emergent structures in the flatfish nursery area play an important role in the ecology of the juvenile flatfishes as feeding ground and/or as refuge from predation. These small-scale aspects of nursery grounds can be considered as EJH and merit attention in habitat suitability models as well as in marine conservation