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.

Temperate marine ecosystems exhibit a marked seasonal variation in environmental conditions that strongly affects the bioenergetics and population dynamics of benthic organisms. As benthic suspension feeders, sponges are subjected to seasonal changes in the supply of their food in the water column. In this study, we examined the temporal variation in the concentration of the picoplanktonic food particles present in the water column and their retention by 3 common demosponges (Crella incrustans, Haliclona venustina and Strongylacidon sp.) from the south coast of Wellington, New Zealand. We sampled 3 times each year over a 2 yr period to examine temporal variation in particle retention efficiency and in the number of particles retained by each species relative to the abundance of particles in the water column. Our results showed that the picoplanktonic species composition and abundance in the water column changed seasonally and between years, as did sponge retention efficiencies and amounts of the available picoplanktonic organisms retained. Averaged across a year, the consumption of non-photosynthetic bacteria is likely to provide the study species with between 20 and 40 times more carbon than the consumption of Synechococcus and Prochlorococcus (marine cyanobacteria). Although the concentration of food particles in the water column positively correlated with the amount of particles retained across all species, we found that retention efficiency did not change with particle concentration. This suggests that retention efficiency is independent of ambient particle concentration, and sponges are unable to increase their particle capture efficiency when food concentrations are lower (e.g. during winter months) and are therefore likely to be susceptible to low levels of food availability.

No abstract

Sponges are an important component of benthic ecosystems in New Zealand, and as suspension feeders they can process large volumes of water meaning that their interaction with the water column is likely to be of great importance. Our research focuses on the functional role of sponges as suspension feeders in temperate rocky subtidal ecosystems on the Wellington South Coast, New Zealand. We investigated the diet composition of two common species of calcareous sponges (Leucosolenia echinata and Leucetta sp.) by identifying and quantifying food particles from water samples using flow cytometry, and estimating the removal efficiency for these species. The natural diet of both species included heterotrophic bacteria, Prochlorococcus sp. and Synechococcus sp., similar to that previously reported for demosponges. We found significant differences in the number of picoplanktonic organisms present between ambient and exhalent water for both study species. Prochlorococcus and Synechococcus were removed with the highest efficiency irrespective of sponge species (52-57%). Both species had similar overall removal efficiencies, but we detected significant differences in the removal rates of the three types of bacteria in each species. Our study is the first to investigate the natural diet of calcareous sponges in temperate rocky subtidal reefs using flow cytometry and we provide evidence for differences in the diets of calcareous sponges and demosponges.

Major nutrients such as phosphate, nitrate, ammonium and silicate, are involved in the metabolic processes of marine organisms. Sponges take up and produce inorganic nutrients and the extent at which they affect the budgets available for other organisms has received little attention. For this reason, we investigated nutrient fluxes for several sponge species in order to estimate whether sponges were net producers or consumers of nutrients from the water column, and how these patterns changed over time. Nutrient fluxes were examined on the south coast of Wellington, New Zealand. For the nutrient analysis (nitrate, nitrite, ammonium, phosphate and silicate), water samples were collected in situ from the inhalant and exhalant water of different sponge species. Samples were analysed both in a multi-species survey and over a two-year period for three other species to determine any temporal changes in fluxes. Our results yielded significant differences in nutrient concentrations between the inhalant and exhalant water for some of the species, but there was no clear pattern associated with the time of year. The levels of dissolved inorganic nutrients in the ambient water varied considerably over the 2-year study period. It is possible that a lack of a clear pattern of nutrient uptake/release of nutrients in some of the study species, and the fact that not all species showed significant uptake/release at different times of the year, may be related to high levels of temporal and spatial variation in the ambient nutrient availability, as well as other temporal fluctuations in parameters, such as water temperature, sponge size, and concentration of food in the water column. Finally, we believe that the activity of specific microbial communities associated with these sponges may be important in explaining the fluxes we have reported.