Abstract
Despite the importance of trophic interactions between organisms, and the relationship between primary production and benthic diversity, there have been few studies that have quantified the carbon flow from pelagic to benthic environments as a result of the assemblage level activity of suspension-feeding organisms. In this study, we examine the feeding activity of seven common sponge species from the Taputeranga marine reserve on the south coast of Wellington in New Zealand. We analysed the diet composition, feeding efficiency, pumping rates, and the number of food particles (specifically picoplanktonic prokaryotic cells) retained by sponges. We used this information, combined with abundance estimates of the sponges and estimations of the total amount of food available to sponges in a known volume of water (89,821 m3), to estimate: (1) particulate organic carbon (POC) fluxes through sponges as a result of their suspension-feeding activities on picoplankton; and (2) the proportion of the available POC from picoplankton that sponges consume. The most POC acquired by the sponges was from non-photosynthetic bacterial cells (ranging from 0.09 to 4.69 g C d−1 with varying sponge percentage cover from 0.5 to 5%), followed by Prochlorococcus (0.07 to 3.47 g C d−1) and then Synechococcus (0.05 to 2.34 g C d−1) cells. Depending on sponge abundance, the amount of POC that sponges consumed as a proportion of the total POC available was 0.2–12.1% for Bac, 0.4–21.3% for Prochlo, and 0.3–15.8% for Synecho. The flux of POC for the whole sponge assemblage, based on the consumption of prokaryotic picoplankton, ranged from 0.07–3.50 g C m2 d−1. This study is the first to estimate the contribution of a sponge assemblage (rather than focusing on individual sponge species) to POC flow from three groups of picoplankton in a temperate rocky reef through the feeding activity of sponges and demonstrates the importance of sponges to energy flow in rocky reef environments.
Highlights
The trophic relationships between benthic and pelagic communities mainly depend on the movement of primary production in surface waters to deeper layers [1]
There has been an increasing interest in the role that benthic suspension-feeders play in the flow of energy between the water column and the benthos
Our study is the first to estimate the contribution of a sponge assemblage to the particulate organic carbon (POC) flow in a temperate rocky reef through the sponges’ in situ feeding activities
Summary
The trophic relationships between benthic and pelagic communities mainly depend on the movement of primary production in surface waters to deeper layers [1]. Benthic marine food webs are essential biological components of coastal ecosystems because of their role in organic matter cycling and because they provide a link between the water column, benthic organisms and sediments [4]. Suspension-feeding invertebrates play an important role in the flow of carbon through marine ecosystems as they have the ability to control the cycling of nutrients, organic matter, plankton and detritus [6,7,8], and move carbon from the pelagic environment to the benthos (and vice versa). Studying the feeding ecology of these organisms is important for understanding the dynamics of particles in the water column and energy flow in marine ecosystems. Sponges may act as a carbon sink, since many species are unpalatable to potential predators and long-lived [17,18]
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