Abstract
Through their tissues or activities, engineer species create, modify, or maintain habitats and alter the distribution and abundance of many plants and animals. This study investigates key ecological functions performed by an engineer species that colonizes coastal ecosystems. The gregarious tubiculous amphipod Haploops nirae is used as a biological model. According to previous studies, the habitat engineered by H. nirae (i.e., Haploops habitat) could provide food and natural shelter for several benthic species such as benthic diatoms belonging to the gender Navicula, the micrograzer Geitodoris planata, or the bivalve Polititapes virgineus. Using data from scientific surveys conducted in two bays, this study explored whether (1) the Haploops sandy‐mud community modifies invertebrate and ichthyologic community structure (diversity and biomass); (2) H. nirae creates a preferential feeding ground; and (3) this habitat serves as a refuge for juvenile fish. Available Benthic Energy Coefficients, coupled with more traditional diversity indices, indicated higher energy available in Haploops habitat than in two nearby habitats (i.e., Sternaspis scutata and Amphiura filiformis/Owenia fusiformis habitats). The use of isotopic functional indices (IFIs) indicated (1) a higher functional richness in the Haploops habitat, related to greater diversity in food sources and longer food chains; and (2) a higher functional divergence, associated with greater consumption of a secondary food source. At the invertebrate‐prey level, IFIs indicated little specialization and little trophic redundancy in the engineered habitat, as expected for homogenous habitats. Our results partly support empirical knowledge about engineered versus nonengineered habitats and also add new perspectives on habitat use by fish and invertebrate species. Our analyses validated the refuge‐area hypothesis for a few fish species. Although unique benthic prey assemblages are associated with Haploops habitat, the hypothesis that it is a preferential feeding area was not verified. However, specialist feeding behavior was observed for predators, which calls for further investigation.
Highlights
Coastal and estuarine systems occupy only approximately 6% of marine surface area but are among the most productive areas on earth (Costanza et al, 1997)
Using a preliminary map of the seabed in the two bays, we identified the three aforementioned habitats and selected 12 stations per bay to compare the ecological roles of the Haploops habitat with the adjacent uncolonized Sternaspis and Amphiura/Owenia habitats
This study investigated functional roles of engineered habitats, using the particular case of H. nirae and the habitat it creates in shallow marine water
Summary
Coastal and estuarine systems occupy only approximately 6% of marine surface area but are among the most productive areas on earth (Costanza et al, 1997) These systems are associated with strong economic and social issues as they have high human population densities while providing numerous ecosystem functions and services (MEA, 2005). In several bays and archipelagos, muddy sediments are extensively colonized by a gregarious tubiculous amphipod, Haploops nirae (Amphipoda)—often confused with H. tubicola (Rigolet, Dubois, Droual, Caisey, & Thiébaut, 2012) This engineer species occurs in high densities and actively modifies the sediment-water interface through tube-building and filtering activities (Rigolet, Le Souchu, Caisey, & Dubois, 2011). We discuss the functional roles of H. nirae, our model engineer species, in comparison with examples from the literature
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