DOI: 10.5061/dryad.02v6wwqb3
title: Competition for waterborne food resources among tropical shallow-water sponges

description: We examined filtration by sponge assemblages in the shallow waters (~2 m
 depth) of Florida Bay (Florida, USA), where water residence times are
 often high and filtration by dense communities of sponges were
 hypothesized to deplete the water column of food, primarily picoplankton
 and dissolved organic matter (DOM). We transplanted three sponge species
 into replicate locations that differed by an order of magnitude in natural
 sponge community biomass. Sponge transplants were clones, enabling us to
 control for sponge genotype effects across all sites. The growth of sponge
 clones was recorded seasonally for 18 – 30 months. Growth of transplants
 placed in areas devoid of sponges was 10 times greater than in areas with
 dense sponge communities, and three times greater than in areas with
 average sponge biomass. Sponge mortality was similar regardless of
 background sponge density. Measures of picoplankton, DOM, and PO4
 concentration confirmed an inverse relationship with sponge community
 biomass, whereas nitrogen concentrations in seawater were highest where
 sponge species replete with nitrogen-fixing symbiotic microbial
 communities were most abundant. This is striking evidence that filtration
 of waterborne resources by sponges in shallow, coastal environments can
 deplete those resources sufficiently to cause exploitative competition
 that limits sponge growth, with cascading implications for tropical
 hardbottom environments where sponges dominate the animal biomass.
description: <em>Study Sites and Experimental
 Set-up</em> Our study sites were located in the
 shallow, coastal waters of the Florida Keys (Fig. 1), an archipelago south
 of Florida (USA) where seagrass and hard-bottom habitats prevail behind a
 250 km long barrier coral reef. Hard-bottom covers ~ 30% of the shallow
 seafloor in the region (Zieman et al., 1989; Herrnkind et al., 1997) and
 is characterized by low relief, limestone bedrock overlain by a thin
 veneer of sediment (Schomer and Drew, 1982; Chiappone, 1996).
 Approximately 60 species of sponges occur in this back-reef region where
 their densities can exceed 80,000 sponges/ha with some individuals
 exceeding 1 m in diameter (Torres et al., 2006; Stevely et al., 2010,
 2011; Butler et al., 2021). Depth at our study sites was ~ 2m, which is
 typical for the shallow seas surrounding the Florida Keys, and all sites
 were separated by a minimum of 0.5 km (Fig. 1). Water turnover and
 vertical mixing in this region of the Florida Keys is largely wind driven
 (Wang et al., 1994; Nuttle et al., 2003; Gilbert et al., 2009; Lee et al.,
 2016), except near channels where tidal mixing predominates. Our study
 sites were at least 3km  from channels andexperienced similar current
 velocities (3 – 12 cm/s) as measured at each site using a WaterMark USGS
 current meter (Model 6205) during spring tides in March 2016.
   We initially began our study with two
 species of HMA sponge common to the region (<em>Ircinia campana
 </em>- Vase sponge; <em>Spongia barbara </em>- Yellow
 sponge) that were transplanted into sites with either medium or high
 natural densities of sponges where their growth was monitored for 30
 months; 18 months into the study we added a third sponge species
 (<em>Spongia graminea</em> - Glove sponge). To control for
 genotype, large sponges of each species were collected from the seafloor
 and cut into 12-15 smaller pieces (~ 3500 cm<sup>3</sup> each)
 that we attached to brick baseplates with plastic cable ties and numbered
 tags. These “clones” were left on the sea floor at the collection site for
 two months to heal and affix to the brick baseplates prior to relocation
 (Fig. 2). After the healing period, clones were out-planted equally onto
 six transplant sites that differed in natural sponge abundance (i.e.,
 medium and high sponge abundance) to test for site-specific differences in
 the growth of sponge out-plants. Prior to out-planting
 sponges, divers surveyed each site to document the density, biomass, and
 diversity of natural sponges that occurred on the sites. Following
 established methods for hard-bottom surveys (Butler et al., 1995, 2018;
 Herrnkind et al., 1997), divers identified, counted, and measured (height,
 diameter) all sponges &gt; 20cm diameter within four, non-overlapping
 25 m x 2 m belt transects positioned haphazardly on each site. “Site” is
 the replicate for the sponge density treatments, so an average from the
 data from the four transects/site was calculated to represent the values
 for each site. Those data were used to compare sponge diversity, density,
 and volume among sites (n = 3 sites per sponge density treatment). The
 volume of sponges counted on the seafloor were estimated based on their
 shapes and volume formulae those shapes (e.g., sphere, cylinder, tube,
 hollow cone, etc.). Prior to out-planting, we used the same measurements
 and formulae to estimate the volume of our clone out-plants.
 To begin the experiment, individually tagged sponge clones (14
 of <em>I. campana</em> and <em>S. barbara</em>)
 were transplanted in March 2016 in a haphazard arrangement within a
 30m<sup>2</sup> area on each of the six medium and high
 natural sponge density sites. Sponge clones were remeasured approximately
 every six months for 18 months: August 2016, March 2017, August 2017. A
 year into the study we added another species (<em>S.
 graminea</em>) to the study and thereafter continued to monitor the
 growth of all three sponge species at the six study sites every 6 months
 for another 12 months (i.e., a total of 30 months of monitoring for
 <em>I. campana</em> and <em>S. barbara</em>; and
 18 months of monitoring of <em>S. graminea</em>). We consider
 the growth measured each March as indicative of “winter” growth (Sept –
 March) and the measurements made in August as indicative of “summer”
 growth (April – August). During each measurement, sponges and the bricks
 to which they were attached were cleaned of epizoic organisms. Near the
 end of the study, we took advantage of a sponge die-off event that
 decimated over 90% of the sponges over a large (500
 km<sup>2</sup>), thus allowing us to test sponge growth under
 a third treatment condition (low natural sponge density) into which all
 three sponge species were transplanted.  We monitored the growth of those
 transplanted sponges only once, 6 months after transplantation, because a
 second sponge-killing cyanobacteria bloom swept over the area again
 killing all of our transplanted sponges and precluding further
 measurements. Mortality of sponges was also monitored during the
 study. Water Column
 Characteristics To document the potential
 relationship between sponge effects on water column characteristics at
 each experimental site, we took water samples at each site in August 2017
 at slack tide during a week in which prevailing winds were less than 5
 kts. A total of 1 liter of seawater was collected in high-density
 polyethylene bottles 1 m from the seafloor by sampling 200 ml of water
 from five locations within each 30 m<sup>2 </sup>experimental
 area on each site. Storage and preservation of water samples followed
 methods presented in McMurray et al. (2016). In the laboratory, water was
 filtered using pre-combusted, 7 micron GF/F filters and 100 ml aliquots
 were stored in centrifuge tubes at -20 °C for nutrient analysis. To
 quantify the concentrations of POM and DOM at sites of varying sponge
 densities, seawater was filtered through pre-combusted, 7 micron GF/F
 filters. Filters were wrapped in aluminum foil and frozen, and 20 ml of
 filtrate was stored in acidified (100 ul of 50% phosphoric acid) glass
 vials at -20 °C. Total dissolved nitrogen (TDN) was quantified using an
 Antek 9000N analyzer that was run in tandem with the Shimadzu TOC 5050
 used to measure DOC. Particulate organic carbon and nitrogen (POC and PON,
 respectively) were measured using a CE Elantech NC2100 elemental analyzer.
 Nutrients (nitrate-nitrite, ammonia, phosphate) were measured with a
 Bran+Luebbe AutoAnalyzer III, and dissolved organic nitrogen was
 calculated as the difference between TDN and dissolved inorganic nitrogen
 (DIN). In addition, 5 mL water subsamples were
 preserved in electron microscopy grade glutaraldehyde (0.1% final
 concentration), frozen in liquid nitrogen after 10 minutes, and stored at
 -80 °C for analysis of picoplankton concentrations.  Phytopicoplankton
 (picoeukaryotes, <em>Synechococcus</em>,
 <em>Prochlorococcus</em>) were enumerated using a BD
 FACSCelesta Flow Cytometer as previously described (McMurray et al., 2018)
 and aliquots of each sample were stained with Sybr Green-1 to quantify
 high nucleic acid (HNA) bacteria, low nucleic acid (LNA) bacteria, and
 viruses. Live particulate organic matter for each picoplankton cell type
 was estimated using standard cell conversions used in previous studies of
 sponge feeding (McMurray et al., 2018).
description: # Dryad dataset Dataset DOI:
 [10.5061/dryad.02v6wwqb3](10.5061/dryad.02v6wwqb3) ## Description of the
 data and file structure field surveys and sponge transplant growth and
 mortality experiment. ### Files and variables #### File:
 Data\_for\_Dryad.xlsx | WATER QUALITY DATA | | |
 :---------------------------------- |
 :----------------------------------------------------------------- | |
 Column titles | Description | | Sponge Site Treatment | low, medium, or
 high sponge abundance on that field site | | Peuk | Concentration of
 picoeukaryotes; x 1000 cells/ml | | Pro | Concentration of
 Prochlorococcus; x 10,000 cells/ml | | Syn | Concentration of
 Synechococcus; x 10,000 cells/ml | | HNA | Concentration of high nucleic
 acid bacteria; x 100,000 cells/ml | | LNA | Concentration of low nucleic
 acid bacteria; x 100,000 cells/ml | | Vir | Concentration of viruses; x
 100,000 cells/ml | | POC | Concentration of particulate organic carbon; uM
 | | POM | Concentration of particulate organic matter; uM | | PO4 |
 Concentration of phosphate; uM | | NOx | Concentration of nitrate/nitrite;
 uM | | NH4 | Concentration of ammonia:uM | | | | | **6 MONTH GROWTH** | |
 | Column titles | Description | | species | sponge species: Ircinia
 campana, Spongia graminea, Spongia barbara | | Sponge site treatment |
 low, medium, or high sponge abundance on that field site | | % increase in
 volume after 6 months | self explanatory | | | | | **SPONGE MORTALITY 18
 MOS** | | | Column titles | Description | | Species | sponge species:
 Ircinia campana, Spongia graminea, Spongia barbara | | Density Treatment |
 low, medium, or high sponge abundance on that field site | | % survival 18
 mos | self explanatory | | | | | **FIELD SURVEYS** | | | Column titles |
 Description | | Site Name | self explanatory | | Latitude | self
 explanatory | | Longitude | self explanatory | | Species | sponge species
 | | Count/100 m | number of sponges of that species per 100 square meters
 | | Volume | volume of sponges of that species per 100 square meters |