Seagrass Edge Research Articles

Blue carbon dynamics across a salt marsh-seagrass ecotone in a cool-temperate estuary

Abstract Background Seagrass and salt marsh ecosystems are recognised for their role in climate change mitigation and adaptation given their carbon storage potential. However, factors driving variability in blue carbon ecosystems are understudied, yet are important to account for. Aims Examine the variability of sediment organic carbon (SOC) and its drivers (seagrass morphometrics and sediment nutrients) at different spatial scales; > 1 km, ~ 150 m and ~ 10 m across the salt marsh-seagrass ecotone. Methods We collected the top 5 cm of sediment in the Olifants River Estuary, a cool-temperate system in South Africa. Using a line transect approach, we sampled across the salt marsh-seagrass ecotone (~ 10 m) in triplicate transects (~ 50 m apart) at three sampling sites (1–3 km) and analysed for SOC and elemental nutrient (nitrogen and phosphorus) content. Seagrass morphometrics (shoot density, leaf length and number per shoot) were measured. Results There was significant (P < 0.05) spatial heterogeneity in SOC stocks between sites (1–3 km) and between salt marshes and seagrass, but low variability at ~150 m. We detected a significant decrease in SOC from salt marsh towards the seagrass edge, with seagrass SOC remaining uniform. Nitrogen content was positively correlated with SOC in seagrass and salt marshes (P < 0.05), but seagrass morphometrics were not significant drivers of SOC. Conclusions The dynamics of blue carbon differ between salt marshes and seagrass, with spatial heterogeneity of SOC at scales > 1 km, suggesting that future BC assessments need to account for spatial heterogeneity to improve the accuracy of carbon removal estimates.

Edge effects of a fragmented seagrass habitat on flow, bivalve recruitment, and sediment dynamics

In both continuous and fragmented seagrass ecosystems, the vegetation edge can be a location of abrupt hydrodynamic change, with impacts to both ecological and physical processes. We address how flow and wave activity change across seagrass meadow edges and the effects of vegetation on sediment dynamics and bivalve recruitment. Two Zostera marina seagrass meadow sites were monitored: a high-density site with >500 shoots m-2 and a low-density site with <250 shoots m-2. Mean flow velocities were significantly reduced in seagrass vegetation adjacent to edges, with reductions compared to unvegetated areas ranging from 30-75%. Recruitment of juvenile bivalves was significantly elevated within vegetation. No significant differences in wave activity or sediment suspension and/or deposition were found spatially across a 10 m distance from a seagrass edge, but significant temporal variability was observed, caused by periodic storms. Wave height was a major predictor for sediment movement along seagrass edges, with an observed 10-fold increase in sediment collection within benthic traps following severe storms. These results were found across various heterogeneous edge configurations and reveal abrupt hydrodynamic responses of both mean flow and turbulence to occur at short spatial scales (1-10 m), with changes to wave and sediment deposition and/or suspension conditions only occurring over larger spatial distances (~100 m). Changes to the hydrodynamic regime were therefore found to be driven by meteorological conditions (e.g. winds, storms) on daily timescales and by changes in seagrass shoot density, altering both bivalve recruitment and sediment dynamics on longer temporal and/or spatial timescales.

Estimating and Applying Fish and Invertebrate Density and Production Enhancement from Seagrass, Salt Marsh Edge, and Oyster Reef Nursery Habitats in the Gulf of Mexico

Seagrasses, oyster reefs, and salt marshes are critical coastal habitats that support high densities of juvenile fish and invertebrates. Yet which species are enhanced through these nursery habitats, and to what degree, remains largely unquantified. Densities of young-of-year fish and invertebrates in seagrasses, oyster reefs, and salt marsh edges as well as in paired adjacent unstructured habitats of the northern Gulf of Mexico were compiled. Species consistently found at higher densities in the structured habitats were identified, and species-specific growth and mortality models were applied to derive production enhancement estimates arising from this enhanced density. Enhancement levels for fish and invertebrate production were similar for seagrass (1370 [SD 317] g m–2 y–1for 25 enhanced species) and salt marsh edge habitats (1222 [SD 190] g m–2 y–1, 25 spp.), whereas oyster reefs produced ~650 [SD 114] g m–2 y–1(20 spp). This difference was partly due to lower densities of juvenile blue crab (Callinectes sapidus) on oyster reefs, although only oyster reefs enhanced commercially valuable stone crabs (Menippe spp.). The production estimates were applied to Galveston Bay, Texas, and Pensacola Bay, Florida, for species known to recruit consistently in those embayments. These case studies illustrated variability in production enhancement by coastal habitats within the northern Gulf of Mexico. Quantitative estimates of production enhancement within specific embayments can be used to quantify the role of essential fish habitat, inform management decisions, and communicate the value of habitat protection and restoration.

Zooplankton in seagrass and adjacent non-seagrass habitats in Tun Mustapha Park, Sabah, Malaysia

A comparison of zooplankton abundance and community in the seagrass and non-seagrass areas of Limau-limauan and Bak- Bak waters within the newly established Tun Mustapha Marine Park was made during 15-17 May 2017. Samples were collected via horizontal tow of a 140 μm plankton net. Environmental variables (temperature, salinity, DO, pH, turbidity) showed no significant differences among the study sites. However, zooplankton showed increasing abundance from non-seagrass, seagrass edge, to seagrass areas at Limau-limauan, while abundance values were comparable among the stations at Bak-bak. Overall zooplankton abundance was significantly higher at the seagrass areas relative to the non-seagrass station at Limau-limauan (p < 0.005), while no statistical difference was found at Bak-Bak (p < 0.21). Mean canopy height was 3-fold higher (p < 0.001) at Limau-limauan than Bak-Bak, suggesting the importance of seagrass bed structural complexity in habitat preference for zooplankton. Cluster analysis revealed the zooplankton community from the seagrass area at Limau-limauan was different from that at seagrass edge and non-seagrass areas, which may be attributed to the influence of seagrass meadows in forming characteristic zooplankton compositions. Marked differences in zooplankton composition and abundance even in close vicinity of sites suggest the importance of local small-scale variations in seagrass habitats in shaping the zooplankton community.

Evidence of surplus carrying capacity for benthic invertebrates with the poleward range extension of the tropical seagrass Halophila decipiens in SE Brazil

Seagrasses may enhance the abundance and diversity of benthic invertebrates through trophic facilitation. We investigated this potential ecological function for two seagrasses in SE Brazil: Halodule emarginata, a native species, and Halophila decipiens, a tropical seagrass recently established in the region. At Halophila sites, the organic matter (or carbon) in sediments decreased steadily from seagrass patches to isolated bare grounds, indicating surplus primary production. This was not observed at Halodule sites. At one of the two Halophila sites, localized trophic enrichment was also consistently linked to increased invertebrate abundance within patches, chiefly through increased carrying capacity of small mesoherbivores. Rather than spillover, edge effects were observed at bordering bare habitats, where polychaete predators were abundant. The transition from seagrass edges to isolated bare habitats was marked by an increase of the density of sipunculid worms. The current spread of Halophila may thus change the spatial distribution of benthic ecological functions.

Morisita's index of patchiness and edge effects: A response to Butturi-Gomes and Petrere (2020)

Abstract In a recent paper in Ecological Indicators, Butturi-Gomes and Petrere (2020) investigated Morisita's index of patchiness in relation to edge effects and concluded: that edge avoidance by a species drives its patchiness estimation … which might be the reason behind so many claims of population aggregation' and that 'the presence of edge avoidance leads to false claims of population aggregation, based solely on Morisita's patchiness index. One of the patchiness 'claims' that they specifically criticised was that of Barnes and Laurie (2018) for intertidal seagrass macrobenthos, Butturi-Gomes and Petrere stating that these authors: disregarded possible edges, which are indeed hard to define in marine environments, but are still of importance, particularly in seagrass substrates, as Smith et al. (2008) pointed out. What Butturi-Gomes and Petrere failed to mention, however, was (a) that Barnes and Laurie did not use Morisita's patchiness index, (b) that the index they did use was not the sole basis for their finding of patchiness, and (c) that they cited extensive previous work at their site that had investigated seagrass edge effects — indeed, rather than ignoring such edges they specifically sited their study area within a non-edge zone (sensu Smith et al., 2008). The patchiness they observed was not 'false' and it was not driven by active aggregation away from edges but most likely by the effect of predation by mobile nekton on prey densities.

Investigating the Functional Role of an Artificial Reef Within an Estuarine Seascape: a Case Study of Yellowfin Bream (Acanthopagrus australis)

Estuaries contain mosaic habitats which support fish across different life stages. Artificial reefs represent a form of habitat enhancement which can provide additional structure for fishes and improve fishing opportunities, but the role of artificial reefs within the broader estuarine seascape has not been extensively studied. We used a VEMCO Positioning System (VPS) to monitor the fine-scale movements of yellowfin bream (Acanthopagrus australis, referred to as Bream), an estuarine predator and important recreational species. Fish were implanted with acoustic tags with accelerometer sensors (to measure relative fish activity), and their movements monitored on an artificial reef and adjacent habitats. Elevated activity patterns during crepuscular periods indicated that foraging was likely occurring over a large seagrass bed adjacent to the artificial reef system. Alternatively, lower activity was observed when fish were on the artificial reef, which may reflect the role of this habitat as a refuge, or that alternative foraging strategies were being employed. All fish exhibited a high degree of fidelity to the artificial reef on which they were tagged, and there was minimal movement among other reef groups within the array. There was extensive overlap in space use contours for smaller fish on the seagrass edge, but no overlap for larger fish that also tended to forage further afield. These findings have implications for the way in which artificial reefs support fish production, especially the importance of connectivity with other key habitats within the estuarine seascape.

Ecological trade-offs in seascape ecology: bay scallop survival and growth across a seagrass seascape

In marine systems, seagrass meadows, which serve as essential nursery and adult habitat for numerous species, experience fragmentation through both human activity and environmental processes. Results from studies involving seagrass patch size and edge effects on associated fauna have shown that patchy seagrass habitats can be either beneficial or detrimental. One reason for the variable results might be the existence of ecological trade-offs for species that associate with seagrass habitats. Bay scallops, Argopecten irradians, are useful model organisms for studying the response of a semi-mobile bivalve to changes in seagrass seascapes—they exhibit a strong habitat association and seagrass offers a predation refuge at a cost of reduced growth. This study investigated the potential ecological survival–growth trade-off for bay scallops living within a seagrass seascape. Scallop growth was consistently fastest in bare sand and slowest at patch centers, and survival showed the opposite trend. Scallops in patch edges displayed intermediate growth and survival. Using models for minimizing mortality (μ) to foraging (f) ratios, the data suggests seagrass edge habitat offered similar value to patch centers. Further, investigations of core-area index suggest that small, complex patches might offer scallops a balance between predation risk and maximized growth. Taken in sum, these results suggest that edge habitats may benefit organisms like bay scallops by maximizing risk versus reward and maximizing edge habitat.

Spatial distribution and nutritional requirements of the endosymbiont-bearing bivalve Loripes lacteus (sensu Poli, 1791) in a Mediterranean Nanozostera noltii (Hornemann) meadow

Sulphur-oxidising endosymbiont-bearing bivalves often inhabit seagrass meadows, where they can control sulphide levels and variably contribute to carbon cycling, by feeding on endosymbiotic bacteria and/or on particulate organic matter from the water column. The patterns of variability in their feeding mode and their spatial distribution within the seagrass meadows are however poorly studied. Seagrass beds form naturally patchy habitats with seagrass-sand edges that may have variable effects on different organisms. The present study aims at understanding differences in feeding mode and abundance of the endosymbiont-bearing bivalve Loripes lacteus (sensu Poli, 1791) as well as the physiological conditions of its endosymbiotic populations between edge and inner portion of meadows of the eelgrass Nanozostera noltii (Hornemann). In July 2010, Loripes specimens were sampled in 4 eelgrass patches at 2 different locations in the Thau lagoon, South of France. There was a clear negative edge effect on the abundance of small individuals of Loripes, while large individuals were homogeneously distributed between edge and inner part of the meadow. Although Loripes isotopic signatures (δ13C and δ15N) were always closer to those of its symbiotic bacteria than to those of suspension-feeding bivalves, eelgrass edge enhanced mixotrophic behaviour of small animals, which assimilated less bacterial carbon and nitrogen at the edge than in the inner part of the eelgrass meadow. No differences related to eelgrass edges were instead found for the bacterial populations harboured by Loripes. Rather, flow cytometry revealed large variability at small spatial scales. Although bacteria were always important for the nutrition of Loripes, these findings showed that seagrass edges may contribute to regulate feeding mode and population structure of Loripes, which may have implications for seagrass functioning.

Seagrass edge effects on fish assemblages in deep and shallow habitats

Shallow seagrass is an important habitat for many fish species, but little is known about fish distribution in deep seagrass or if depth affects fish distribution within patches. Using stereo video, fish distribution patterns in Port Phillip Bay, Australia, were examined in deep (3.5–6 m) and shallow (<1.5 m) areas over four months (December–March). Three positions were sampled in relation to seagrass patches; the interior of seagrass patches, at the edge of seagrass patches and over sand distant (>100 m) from seagrass. Recorded video was subsequently analysed using time in view (TiV) and MaxN, with fish showing strong responses to both depth and habitat type. Fish assemblages were different between deep and shallow seagrass, and many species were found only in shallow (e.g. Australian salmon, King George whiting, southern garfish) or deep (e.g. bridled leatherjackets, goatfish) seagrass. King George whiting spent more time at the edge than the middle of shallow patches, while TiV and MaxN indicated that garfish and odacids were more common in the middle than the edge of patches. Few species were observed over sand. Overall fish lengths were greater in shallow than deep seagrass and at the edge than middle of patches. Edge effects were found to occur in both deep and shallow seagrass and should be considered when designing sampling regimes and determining conservation strategies.

Balancing the edge effects budget: bay scallop settlement and loss along a seagrass edge

Edge effects are a dominant subject in landscape ecology literature, yet they are highly variable and poorly understood. Often, the literature suggests simple models for edge effects-positive (enhancement at the edge), negative (enhancement at the interior), or no effect (neutral)--on a variety of metrics, including abundance, diversity, and mortality. In the marine realm, much of this work has focused on fragmented seagrass habitats due to their importance for a variety of commercially important species. In this study, the settlement, recruitment, and survival of bay scallops was investigated across a variety of seagrass patch treatments. By simultaneously collecting settlers (those viable larvae available to settle and metamorphose) and recruits (those settlers that survive some period of time, in this case, 6 weeks) on the same collectors, we were able to demonstrate a "balance" between positive and negative edge effects, resulting in a net neutral effect. Scallop settlement was significantly enhanced along seagrass edges, regardless of patch type while survival was elevated within patch interiors. However, recruitment (the net result of settlement and post-settlement loss) did not vary significantly from edge to center, representing a neutral effect. Further, results suggest that post-settlement loss, most likely due to predation, appears to be the dominant mechanism structuring scallop abundance, not patterns in settlement. These data illustrate the complexity of edge effects, and suggest that the metric used to investigate the effect (be it abundance, survival, or other metrics) can often influence the magnitude and direction of the perceived effect. Traditionally, high predation along a habitat edge would have indicated an "ecological trap" for the species in question; however, this study demonstrates that, at the population level, an ecological trap may not exist.

Influence of tides on assemblages and behaviour of fishes associated with shallow seagrass edges and bare sand

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 456:187-199 (2012) - DOI: https://doi.org/10.3354/meps09695 Influence of tides on assemblages and behaviour of fishes associated with shallow seagrass edges and bare sand Alistair Becker1,*, Christine Coppinger1,2, Alan K. Whitfield1 1South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa 2Department of Ichthyology and Fisheries Science, Rhodes University, PO Box 94, Grahamstown 6140, South Africa *Email: a.becker@saiab.ac.za ABSTRACT: Seagrass beds and associated fish assemblages have been the focus of a large number of past studies. However, the influence of small water depth changes due to tides on fish species along shallow seagrass bed edges is unknown. In this study an underwater video camera was deployed to examine the fish community at 3 seagrass edge (Zostera capensis) and 3 sand sites over incoming spring and neap tides in the Bushmans Estuary, South Africa. Small changes in tidally driven water depth had significant effects on the abundance of common fish taxa, with gobies decreasing and others, including mullets, increasing in abundance. These general patterns were consistent in both seagrass and sand sites, as well as during spring and neap tidal cycles. There were inconsistent differences in the abundance of common fish taxa between seagrass edges and bare sand. Importantly, when differences did occur, these were contingent on tidal stage or linked to different tidal cycles (neap or spring), highlighting that small changes in depth may influence edge effects. The behaviour of fish did not appear to be influenced by water depth, but for some taxa there were distinct differences in swimming behaviour between those individuals associated with seagrass beds and those situated over bare sand. These small temporal scale changes in water depth are a previously overlooked aspect of littoral seagrass landscapes that may be important in structuring associated fish communities. KEY WORDS: Underwater video · Water depth · Estuary · Fish movements · Zostera capensis · South Africa Full text in pdf format PreviousNextCite this article as: Becker A, Coppinger C, Whitfield AK (2012) Influence of tides on assemblages and behaviour of fishes associated with shallow seagrass edges and bare sand. Mar Ecol Prog Ser 456:187-199. https://doi.org/10.3354/meps09695 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 456. Online publication date: June 07, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Edge effects in patchy seagrass landscapes: The role of predation in determining fish distribution

Predation is often described as an underlying mechanism to explain edge effects. We assessed the importance of predation in determining edge effects in seagrass using two approaches: a video survey to sample predators at small scales across seagrass edges, and a tethering experiment to determine if predation was an underlying mechanism causing edge effects. Underwater videos were placed at four positions: middle of seagrass patches; edge of seagrass; sand immediately adjacent to seagrass and sand distant from seagrass. Fish abundances and the time fish spent in view were measured. The main predatory fish (Australian salmon, Arripis spp.) spent more time over adjacent sand than other positions, while potential prey species (King George whiting, Sillaginodes punctata (Cuvier), recruits) were more common in the middle of seagrass patches. Other species, including the smooth toadfish, Tetractenos glaber (Freminville), and King George whiting adults, spent more time over sand adjacent to seagrass than distant sand, which may be related to feeding opportunities. King George whiting recruits and pipefish ( Stigmatopora spp.) were tethered at each of the four positions. More whiting recruits were preyed upon at outer than inner seagrass patches, and survival time was greater in the middle of shallow seagrass patches than other positions. Relatively few pipefish were preyed upon, but of those that were, survival time was lower over sand adjacent to seagrass than at the seagrass edge or middle. Video footage revealed that salmon were the dominant predators of both tethered King George whiting recruits and pipefish. The distribution of predators and associated rate of predation can explain edge effects for some species (King George whiting) but other mechanisms, or combinations of mechanisms, are determining edge effects for other species (pipefish).

Resource distribution influences positive edge effects in a seagrass fish

According to conceptual models, the distribution of resources plays a critical role in determining how organisms distribute themselves near habitat edges. These models are frequently used to achieve a mechanistic understanding of edge effects, but because they are based predominantly on correlative studies, there is need for a demonstration of causality, which is best done through experimentation. Using artificial seagrass habitat as an experimental system, we determined a likely mechanism underpinning edge effects in a seagrass fish. To test for edge effects, we measured fish abundance at edges (0-0.5 m) and interiors (0.5-1 m) of two patch configurations: continuous (single, continuous 9-m2 patches) and patchy (four discrete 1-m2 patches within a 9-m2 area). In continuous configurations, pipefish (Stigmatopora argus) were three times more abundant at edges than interiors (positive edge effect), but in patchy configurations there was no difference. The lack of edge effect in patchy configurations might be because patchy seagrass consisted entirely of edge habitat. We then used two approaches to test whether observed edge effects in continuous configurations were caused by increased availability of food at edges. First, we estimated the abundance of the major prey of pipefish, small crustaceans, across continuous seagrass configurations. Crustacean abundances were highest at seagrass edges, where they were 16% greater than in patch interiors. Second, we supplemented interiors of continuous treatment patches with live crustaceans, while control patches were supplemented with seawater. After five hours of supplementation, numbers of pipefish were similar between edges and interiors of treatment patches, while the strong edge effects were maintained in controls. This indicated that fish were moving from patch edges to interiors in response to food supplementation. These approaches strongly suggest that a numerically dominant fish species is more abundant at seagrass edges due to greater food availability, and provide experimental support for the resource distribution model as an explanation for edge effects.

Proximity to rocky reefs alters the balance between positive and negative effects on seagrass fauna

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 405:175-186 (2010) - DOI: https://doi.org/10.3354/meps08516 Proximity to rocky reefs alters the balance between positive and negative effects on seagrass fauna Fernando Tuya1,2,6,*, Mathew A. Vanderklift3, G. A. Hyndes2, T. Wernberg2,4, M. S. Thomsen2,5, C. Hanson2 1CIIMAR, Rúa das Bragas 287, Porto, Portugal 2Centre for Marine Ecosystem Research, Edith Cowan University, Joondalup Drive, 6027 Western Australia, Australia 3CSIRO Marine and Atmospheric Research, Private Bag 5, Wembley, 6913 Western Australia, Australia 4School of Plant Biology, University of Western Australia, Hackett Drive, Crawley, 6009 Western Australia, Australia 5Department of Marine Ecology, National Environmental Research Institution, PO Box 358, 400 Roskilde, Denmark 6Present address: BIOGES, 35017 University of Las Palmas de GC, Canary Islands, Spain *Email: f.tuya@ecu.edu.au ABSTRACT: Proximity to habitat margins can alter the balance between positive and negative forces on species abundance. Based on this idea we examined abundance patterns of herbivorous gastropods in seagrasses adjacent to rocky reefs. We tested whether the balance between the intensity of predation (negative effect) and recruitment of new individuals (positive effect) changes with increasing distance from reefs. Abundances of gastropods varied with distance to reefs, but the direction of changes in abundance was taxon-specific: some taxa decreased in abundance with increasing distance from reefs (e.g. Pyrene bidentata), while others showed the opposite pattern (e.g. Cantharidus lepidus). Predators were more abundant on reefs and in immediately adjacent seagrasses, relative to seagrass meadow interiors. Predation intensity on 2 species with opposite patterns of abundance with proximity to reefs (P. bidentata and C. lepidus) was consistently higher in seagrasses near reef edges than in seagrass interiors, and C. lepidus was more susceptible to predation than P. bidentata. Recruitment of P. bidentata was higher in seagrasses adjacent to reefs relative to seagrass interiors, whereas recruitment of C. lepidus did not vary with distance from reefs. Dispersal of P. bidentata individuals from reefs probably explains the greater recruitment of P. bidentata at seagrass edges relative to interiors; this compensates for losses due to predation, thereby enabling high abundance in seagrasses adjacent to reefs despite suffering greater predation at this distance relative to the interiors of the seagrass meadows. In contrast, losses of C. lepidus due to predation reduced its abundance in seagrasses adjacent to reefs, while recruitment was invariant, so this species was most abundant in seagrass meadow interiors. Thus, proximity to habitat margins affected abundance patterns by influencing mortality (predation) and replenishment (recruitment) of populations. This balance was dependent on species identity, and led to contrasting patterns of abundance among species with proximity to habitat interfaces. KEY WORDS: Cross-habitat exchanges · Gastropods · Habitat connectivity · Predation · Supply-side processes · Edge effects · Habitat linkages · Rocky reefs Full text in pdf format Supplementary material PreviousNextCite this article as: Tuya F, Vanderklift MA, Hyndes GA, Wernberg T, Thomsen MS, Hanson C (2010) Proximity to rocky reefs alters the balance between positive and negative effects on seagrass fauna. Mar Ecol Prog Ser 405:175-186. https://doi.org/10.3354/meps08516Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 405. Online publication date: April 29, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

RESOURCE DISTRIBUTION INFLUENCES POSITIVE EDGE EFFECTS IN A SEAGRASS FISH

According to conceptual models, the distribution of resources plays a critical role in determining how organisms distribute themselves near habitat edges. These models are frequently used to achieve a mechanistic understanding of edge effects, but because they are based predominantly on correlative studies, there is need for a demonstration of causality, which is best done through experimentation. Using artificial seagrass habitat as an experimental system, we determined a likely mechanism underpinning edge effects in a seagrass fish. To test for edge effects, we measured fish abundance at edges (0–0.5 m) and interiors (0.5–1 m) of two patch configurations: continuous (single, continuous 9-m2 patches) and patchy (four discrete 1-m2 patches within a 9-m2 area). In continuous configurations, pipefish (Stigmatopora argus) were three times more abundant at edges than interiors (positive edge effect), but in patchy configurations there was no difference. The lack of edge effect in patchy configurations might be because patchy seagrass consisted entirely of edge habitat. We then used two approaches to test whether observed edge effects in continuous configurations were caused by increased availability of food at edges. First, we estimated the abundance of the major prey of pipefish, small crustaceans, across continuous seagrass configurations. Crustacean abundances were highest at seagrass edges, where they were 16% greater than in patch interiors. Second, we supplemented interiors of continuous treatment patches with live crustaceans, while control patches were supplemented with seawater. After five hours of supplementation, numbers of pipefish were similar between edges and interiors of treatment patches, while the strong edge effects were maintained in controls. This indicated that fish were moving from patch edges to interiors in response to food supplementation. These approaches strongly suggest that a numerically dominant fish species is more abundant at seagrass edges due to greater food availability, and provide experimental support for the resource distribution model as an explanation for edge effects.

Seagrass patch size affects fish responses to edges

1. Patch area and proximity of patch edge can influence ecological processes across patchy landscapes and may interact with each other. Different patch sizes have different amounts of core habitat, potentially affecting animal abundances at the edge and middle of patches. In this study, we tested if edge effects varied with patch size. 2. Fish were sampled in 10 various-sized seagrass patches (114-5934 m(2)) using a small (0.5 m(2)) push net in three positions within each patch: the seagrass edge, 2 m into a patch and in the middle of a patch. 3. The two most common species showed an interaction between patch size and the edge-interior difference in abundance. In the smallest patches, pipefish (Stigmatopora nigra) were at similar densities at the edge and interior, but with increasing patch size, the density at the edge habitat increased. For gobies (Nesogobius maccullochi), the pattern was exactly the opposite. 4. This is the first example from a marine system of how patch size can influence the magnitude and pattern of edge effects. 5. Both patch area and edge effects need to be considered in the development of conservation and management strategies for seagrass habitats.

Seagrass habitat complexity does not always decrease foraging efficiencies of piscivorous fishes

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 377:43-49 (2009) - DOI: https://doi.org/10.3354/meps07869 Seagrass habitat complexity does not always decrease foraging efficiencies of piscivorous fishes Masahiro Horinouchi1,*, Naoki Mizuno2, Yuka Jo2, Masashi Fujita2, Mitsuhiko Sano3, Yuzuru Suzuki2 1Research Center for Coastal Lagoon Environments, Shimane University, 1060 Nishikawatsu-cho, Matsue, Shimane 6908504, Japan 2Fisheries Laboratory, Graduate School of Agricultural and Life Sciences, University of Tokyo, 2971-4 Bentenjima, Maisaka, Hamamatsu, Shizuoka 4310214, Japan 3Laboratory of Global Fisheries Science, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 1138657, Japan *Email: hori@soc.shimane-u.ac.jp ABSTRACT: The foraging efficiencies of predators in relation to seagrass density and microhabitat use patterns of prey during predator presence/absence were examined by laboratory experiments. The foraging efficiency of the permanent resident piscivorous sculpin Pseudoblennius cottoides, which employed ambush and stalk-and-attack tactics, was higher in the presence of seagrass, while that of the transient piscivorous gnomefish Scombrops boops, which employed chase-and-attack tactics, decreased in denser seagrass. When coexisting with gnomefish, juveniles of the prey goby Gymnogobius heptacanthus sometimes entered seagrass areas to avoid attacks by such predators. In the absence of gnomefish, however, goby juveniles almost always stayed outside the seagrass areas (instead inhabiting open areas adjacent to the outer seagrass edge), even when sculpin were absent. These phenomena suggested that dense seagrass may be characterized by a constant potential risk (for prey) resulting from permanent resident predators whose foraging efficiency was improved by the habitat structure. Accordingly, prey species lacking tactics to efficiently decrease risks from such predators may remain outside the seagrass habitat, although close enough to successfully retreat to it in response to acute temporal risks offered by transient chase-and-attack predators. Such differential habitat use patterns corresponding to different predator types may be at least partly responsible for the concentrations of small fishes sometimes observed in open areas adjoining the outer margins of natural seagrass habitats. KEY WORDS: Permanent resident piscivorous fish · Foraging efficiency · Seagrass · Habitat complexity · Prey habitat choice Full text in pdf format PreviousNextCite this article as: Horinouchi M, Mizuno N, Jo Y, Fujita M, Sano M, Suzuki Y (2009) Seagrass habitat complexity does not always decrease foraging efficiencies of piscivorous fishes. Mar Ecol Prog Ser 377:43-49. https://doi.org/10.3354/meps07869 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 377. Online publication date: February 26, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Edge effects on fish associated with seagrass and sand patches

Seagrass beds form naturally patchy habitats with large areas of seagrass-sand inter- face, or edges. Fish were sampled at 3 sites in the temperate waters of Victoria, Australia, using small (0.5 m wide) push nets at 7 positions: unvegetated sand distant from the patch on the seaward side, the sand edge adjacent to the seagrass on the seaward side, the seagrass edge on the seaward side, the middle of the seagrass patch, the seagrass edge on the shore side of the patch, the sand adjacent to the seagrass on the shoreward side of the patch and unvegetated sand distant from the seagrass on the shoreward side. Samples were taken during the day and night, and seagrass variables were col- lected to describe structural complexity. As expected, more fish were caught in seagrass than over sand. Within seagrass, we found strong and consistent patterns at edges. Regardless of site, the total number of fish sampled was greater at the seaward seagrass edge (484 fish) than in the seagrass middle (231), but there was little difference between the seagrass middle and the shoreward seagrass edge (297). Two species of pipefish, Stigmatopora argus (193) and S. nigra (160), were much more abundant at the seaward seagrass edge than in the seagrass middle at all sites (54 and 46, respec- tively). The goby Nesogobius maccullochi showed a very different pattern. It was more abundant at the shoreward seagrass edge (127) than over the seagrass middle (31) at all sites, and tended to be more abundant over sand at the edge of seagrass patches than in any other sand positions. The weed- fish Cristiceps australis was significantly more abundant at the seaward seagrass edge (26) than in the middle (11), but only at night. Consistent patterns in fish distributions demonstrate clear edge effects both within and alongside seagrass at these sites in south-eastern Australia.

ACOUSTIC ECOLOGY OF FORAGING BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS), HABITAT-SPECIFIC USE OF THREE SOUND TYPES

The function(s) of a particular sound can be explored in detail only if the context of its use is well understood. The behavior of the signaler, and the habitat in which that behavior is observed, are two of the most important components of understanding context specific use of a sound. Bottlenose dolphin foraging behavior is often inferred from relatively few behavioral cues that are visible from the surface. To investigate the use of three specific sound types: echolocation, whistles, and pops during foraging, I recorded sound use by animals engaged in a set of previously defined specific foraging behaviors using a system that allowed me to see animals throughout the water column. Lone foraging animals produced all three sounds at significantly higher rates than animals foraging in groups, and the rate of sound production per animal in multi-animal foraging groups did not vary even as the groups reached up to five individuals. Production of echolocation and pops by lone foraging animals accounted for much of the difference. Foraging dolphins also displayed habitat-specific use of particular sound types. They preferentially produced echolocation and pops in the sand habitat and, at least for lone animals, in the seagrass edge habitat.