Trophic Cascades and the Role of the Coralline Algae in Coral Recruitment  (Year 2 of 2) Project Number: CMRC-01-NRRK-01-03C Principle Investigators: Steneck, R. S. Region(s): Lee Stocking Island, Bahamas The resilience of coral reefs depends on coral's ability to settle and survive in reef habitats. Many surfaces on reefs are hostile to settling corals. Coralline algae is thought to induce settlement and recruitment of corals on reefs but it is susceptible to overgrowth by fleshy algae, which is abundant on fished reefs where herbivory is low. This project proposes to compare the recruitment potential of the benthos on fished and unfished reefs in the Bahamas and Belize. In particular the abundance and species composition of crustose coralline algae will be quantified and examined for newly settled corals. Recent research in the Indo-Pacific found over 60% of all reef building corals recruited to a single coralline algae, Titanoderma prototypum. This alga is ubiquitous in the Caribbean but neither it nor any other coralline species has been systematically examined for newly recruited corals. The proposed study will conduct field surveys and deploy coral settlement plates (which will remain for a year to become fouled with corallines and other reef organisms) in a way identical to the recently completed research in the Indo Pacific. This should allow direct comparisons to be made between coral recruitment density and substrate specificity between the two reef systems. Objective 1) To determine if coral spat are associated with reef-dwelling species of encrusting coralline algae. Hypothesis A) To test if the density of surviving coral spat is greatest on coral settlement-inducing coralline species such as Hydrolithon borergesenii. Hypothesis B) To test if the density of surviving coral spat is greatest on the coralline alga Titanoderma prototypum. Objective 2) To determine if coralline abundance, species composition or coral settlement patterns differ inside vs outside no-take reserves. Hypothesis A) To test the hypothesis that algal biomass will be lower and coralline abundance higher inside no-take reserves relative to locally fished areas. Hypothesis B) To test the hypothesis that Titanoderma prototypum abundance will be higher in no-take reserves. Objective 3) To determine if patterns of colonization by algae (especially T. prototypum) and corals on exposed and cryptic microhabitats differs inside vs outside no-take reserves. Hypothesis A) To test the hypothesis that turf and macroalgae will be less abundant on both exposed and cryptic surfaces of coral settlement plates inside no-take reserves. Hypothesis B) To test the hypothesis that Titanoderma prototypum abundance will be most abundant on cryptic (underside) surfaces of coral settlement plates inside no-take reserves. Hypothesis C) To test the hypothesis that coral settlement will be greatest on cryptic surfaces (underside) of no-take reserves.   SEMI-ANNUAL REPORT OBJECTIVES and HYPOTHESES [Interim results in brackets]: Objective 1) To determine if coral spat are associated with reef-dwelling species of encrusting coralline algae Hypothesis A) To test if the density of surviving coral spat is greatest on coral settlement-inducing coralline species such as Hydrolithon boergesenii [Yes, so far. Fig. 2] Hypothesis B) To test if the density of surviving coral spat is greatest on the coralline alga Titanoderma prototypum. [This species has not been found in the Bahamas (but it was collected in Bonaire and Belize] Objective 2) To determine if coralline abundance, species composition or coral settlement patterns differ inside vs. outside no-take reserves Hypothesis A) To test the hypothesis that algal biomass will be lower and coralline abundance higher inside no-take reserves relative to locally fished areas. [No clear support yet] Hypothesis B) To test the hypothesis that Titanoderma prototypum abundance will be higher in no-take reserves [This alga is rare or absent from the reefs studied.] Objective 3) To determine if patterns of colonization by algae (especially T. prototypum) and corals on exposed and cryptic microhabitats of the settlement plates differs inside vs. outside no-take reserves. [Too soon to tell since all of these hypotheses rely on data from the settlement plates.] Hypothesis A) To test the hypothesis that turf and macroalgae will be less abundant on both exposed and cryptic surfaces of coral settlement plates inside no-take reserves. Hypothesis B) To test the hypothesis that Titanoderma prototypum abundance will be most abundant on cryptic (underside) surfaces of coral settlement plates inside no-take reserves Hypothesis C) To test the hypothesis that coral settlement will be greatest on cryptic surfaces (underside) of no-take reserves RESULTS: Within the Bahamas, along Exuma Sound, I established two study sites to quantify rates of coral settlement inside and outside marine protected areas. The MPA site was the Wardrick Wells Reserve and the fished control site was Lee Stocking Island. The sites were surveyed at 5 m and 10 m for coral, algae and other sessile benthic components. Fish will be surveyed in the Fall of 2003 to determine if the marine protected areas function to keep trophic cascades intact. This research is part of a larger Caribbean-wide project in which coral settlement inside and outside MPAs is being studied (Figure 1). Other sites (funded from other sources) are the Bahamas, Bonaire, Yucatan coast of Mexico and Belize. Figure 1. The location and number of coral settlement plates throughout the Caribbean. Coral reefs surveys using a modified AGRRA protocol (line transect) determined the abundance dominant reef organisms at 2 and 10 m Table 1. The surveys are intended to provide data on two factors that drive coral settlement: 1) local abundance of live coral and 2) the recruitment potential of the benthos. The latter tests the hypothesis that fleshy macroalgae on reefs creates a poor environment for newly settled corals and certain species of crustose coralline algae create a good environment for newly settled corals (see hypotheses above). Table 1. Survey results for the two sites in the Bahamas. A. Animal distributions and B. Algal distributions. Algal percent cover times canopy height (“CH” in mm) is used to determine the “algal index” which corresponds to algal biomass. Overall, coral cover was about 25% (ranged 16 – 31%) cover, and macroalgae tended to be somewhat higher (24 – 48% cover; Table 1). Macroalgae was not lower in the marine protected region of the Wardrick Wells reserve (Table 1). Turf algae was abundant in places (e.g. Rainbow and North Norman reefs average 47% turf algae at 6 m. Coralline algae was slightly more abundant in the MPA (averaging between 5 and 10% cover) than it was in the control regions (where it averaged between 2 and 6 %). In general coralline abundance in the Bahamas at the study sites (e.g. Table 1) were lower than elsewhere. For example, Bonaire’s reefs ranged between 10 and 12%. Coralline abundance was determined at the species level. The most abundant corallines also had a higher percent of coral spat but at low abundance (Fig. 2). Figure 2. Coralline abundance from transects (left) and spat abundance on coralline species from collected specimens (right). All 400 coral recruitment plates will be retrieved in the Fall of 2003. PAPERS PRESENTED BASED ON 2002 WORK: None. Work is in progress. MANUSCRIPTS AND PUBLICATIONS: None. Work is in progress. ANNUAL REPORT OBJECTIVES: [updated interim results in brackets] Objective 1) To determine if coral spat are associated with reef-dwelling species of encrusting coralline algae. Hypothesis A) To test if the density of surviving coral spat is greatest on coral settlement-inducing coralline species such as Hydrolithon boergesenii . [small fraction found on H. boergesenii, see Figure 2] Hypothesis B) To test if the density of surviving coral spat is greatest on the coralline alga Titanoderma prototypum. [This species has was not found in the Bahamas (it was found in highest abundance in Bonaire).] Objective 2) To determine if coralline abundance, species composition or coral settlement patterns differ inside vs. outside no-take reserves. Hypothesis A) To test the hypothesis that algal biomass will be lower and coralline abundance higher inside no-take reserves relative to locally fished areas. [analysis still in progress] Hypothesis B) To test the hypothesis that Titanoderma prototypum abundance will be higher in no-take reserves. [This alga is rare or absent from the reefs studied in the Bahamas.] Objective 3) To determine if patterns of colonization by algae (especially T. prototypum) and corals on exposed and cryptic microhabitats of the settlement plates differs inside vs. outside no-take reserves. [analysis still in progress] Hypothesis A) To test the hypothesis that turf and macroalgae will be less abundant on both exposed and cryptic surfaces of coral settlement plates inside no-take reserves. Hypothesis B) To test the hypothesis that Titanoderma prototypum abundance will be most abundant on cryptic (underside) surfaces of coral settlement plates inside no-take reserves. Hypothesis C) To test the hypothesis that coral settlement will be greatest on cryptic surfaces (underside) of no-take reserves. METHODS: Within the Bahamas, along Exuma Sound, two study sites were established to quantify rates of coral settlement inside and outside marine protected areas. The MPA site was the Wardrick Wells Reserve and the fished control site was Lee Stocking Island. The sites were surveyed at 5 m and 10 m for coral, algae and other sessile benthic components. Four hundred terracotta settlement plates (10 x 10 x 1.5 cm) were deployed in August, 2003, inside unfished (MPA) and fished (control) areas at two depths (5 and 10 m) on replicated reefs. Plates were elevated one cm off the substrate and were deployed for over a year in order for all surfaces to become colonized by local reef-dwelling organisms. After 395 days, top, bottom and side surfaces were analyzed microscopically to identify colonizing organisms and to quantify the settlement density, size structure and substrate selectivity of settling corals. Over 95% of the coral settlement occurred in the subcryptic underside of the settlement plates. Plates were surveyed in March 2003, and surveyed again prior to removal in September, 2003. Digital photographs were taken of the top and bottom surfaces of each plate, and analysis of the photos for percent cover is underway. Fish were also surveyed in September, 2003 to determine if the marine protected areas function to keep trophic cascades intact. This research is part of a larger Caribbean-wide project in which coral settlement inside and outside MPAs is being studied (Figure 1). Other sites (funded from other sources) are the Virgin Islands, Bonaire, the Yucatan coast of Mexico, and Belize. The transect surveys were intended to provide data on two factors that drive coral settlement: 1) local abundance of live coral and 2) the recruitment potential of the benthos. The latter tests the hypothesis that fleshy macroalgae on reefs creates a poor environment for newly settled corals and certain species of crustose coralline algae create a good environment for newly settled corals (see hypotheses above). Results of the surveys suggest overall coral cover was about 25% (ranged 16 – 31%) cover, and macroalgae tended to be somewhat higher (24 – 48% cover). Macroalgae was not lower in the marine protected region of the Wardrick Wells reserve. Turf algae was abundant in places (e.g. Rainbow and North Norman reefs average 47% turf algae at 6 m). Coralline algae was slightly more abundant in the MPAs (averaging between 5 and 10% cover) than it was in the control regions (where it averaged between 2 and 6 %). In general, coralline abundance in the Bahamas study sites were lower than elsewhere in the Caribbean. For example, Bonaire’s reefs ranged between 10 and 12%. Coralline abundance was determined at the species level. The most abundant corallines also had a higher percent of coral spat but at low abundance (Figure 2). Following preliminary analysis of the deployed settlement plates, it has been determined that of the five sites surveyed in the Caribbean, the Bahamas is unique. Settlement rates are high, however, settlers are primarily coming from brooders, rather than reef-building broadcasting corals, and Titanoderma prototypum is absent unlike all other sites surveyed in the Caribbean. Post settlement is presumed to be high, as here is a lack of mid to large sized individuals, particularly agaricids, also found in every other region. This could be due in part to frequent storm activity, resulting in increased sedimentation and subsequent smothering of newly settled corals. Figure 3, on the following page, illustrates the average number of spat per tile found in the five Caribbean sites surveyed. The Bahamas was found to have an average of 1.15 spat per tile. Figure 4, shows the breakdown of spat per tile in Bahamian Marine Protected Areas vs. controls. Within the MPAs, numbers of spat per tile averaged 1.5, whereas in the controls there were 0.88 spat per tile. The primary substrate for settlement in the Bahamas is bare substrate, with 80% of spat found settled on bare substrate, followed by encrusted polychaete tubes and corraline encrusted algae (Figure 5). Through the course of the recent research conducted in the Caribbean, it has been found that polychaete worm tubes, in addition to certain species of corraline algaes, are favorable habitats for coral spat. This is made evident in Figure 6, showing the average percent cover of the plate bottoms. Bare substrate is the most available hospitable substrate over time. Early on after deployment, recruitment potential is high, with high percentages of bare substrate and increasing numbers of polychaete tubes available, peaking around day 200. Over time, hostile encrusting organisms (in the case of the Bahamas, nearly all encrusting organisms are hostile, except for polychaete tubes, since favorable corallines are absent), algal turf, and macroalgae take over, contributing to the loss of nursery habitat and creating decreased recruitment potential. Though a high percentage of cover is still bare at the end of the deployment period, analysis showed much of this bare substrate to occur away from the underside edges, thus out of reach for spat settlement. After comparing succession data with that of the other Caribbean regions, it is tempting to speculate that the absence of T. prototypum in the late successional stages, in combination with sedimentation, could be contributing to the high instances of post settlement mortality in the Bahamas. Among the sites surveyed in the Caribbean, coral settlement among and within regions corresponded to environments where rates of parrotfish grazing were high, macroalgal abundances adjacent to the plates were low and colonization (by a myriad of organisms including corallines that facilitate settlement) was high. After further analysis, the theory that some plate-colonizing organisms create poor nursery habitats for coral settlement while others facilitate settlement and post-settlement survival will be expanded upon. It is evident that collapsed trophic cascades that steer succession toward organisms hostile to settling corals may jeopardize the resilience of coral reefs to recover from disturbances. ADDITIONAL PERSONNEL (Students, Other scientists, technicians, etc.): Michelle Paddock, Ph.D student, University of Miami; Lindsay Harrington, Ph.D student, James Cook University; and Suzanne Arnold, Masters student, University of Maine PAPERS PRESENTED BASED ON 2003 WORK: Steneck, RS, Harrington, L, Paddock, MJ, Arnold, SN. (2004) Do trophic cascades facilitate coral settlement on Caribbean reefs? Proceedings of the 10th International Coral Reef Symposium, Okinawa, Japan. [Abstract]. MANUSCRIPTS AND PUBLICATIONS: work in progress

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Updated: May 28, 2004