Seagrasses, marine flowering plants, are widely distributed along temperate and tropical coastlines of the world. Seagrasses have key ecological roles in coastal ecosystems and can form extensive meadows supporting high biodiversity. The global species diversity of seagrasses is low (b60 species), but species can have ranges that extend for thousands of kilometers of coastline. Seagrass bioregions are defined here, based on species assemblages, species distributional ranges, and tropical and temperate influences. Six global bioregions are presented: four temperate and two tropical. The temperate bioregions include the Temperate North Atlantic, the Temperate North Pacific, the Mediterranean, and the Temperate Southern Oceans. The Temperate North Atlantic has low seagrass diversity, the major species being Zostera marina, typically occurring in estuaries and lagoons. The Temperate North Pacific has high seagrass diversity with Zostera spp. in estuaries and lagoons as well as Phyllospadix spp. in the surf zone. The Mediterranean region has clear water with vast meadows of moderate diversity of both temperate and tropical seagrasses, dominated by deep-growing Posidonia oceanica. The Temperate Southern Oceans bioregion includes the temperate southern coastlines of Australia, Africa and South America. Extensive meadows of low-to-high diversity temperate seagrasses are found in this bioregion, dominated by various species of Posidonia and Zostera. The tropical bioregions are the Tropical Atlantic and the Tropical Indo-Pacific, both supporting mega-herbivore grazers, including sea turtles and sirenia. The Tropical Atlantic bioregion has clear water with a high diversity of seagrasses on reefs and shallow banks, dominated by Thalassia testudinum. The vast Tropical Indo-Pacific has the highest seagrass diversity in the world, with as many as 14 species growing together on reef flats although seagrasses also occur in very deep waters. The global distribution of seagrass genera is remarkably consistent north and south of the equator; the northern and southern hemispheres share ten seagrass genera and only have one unique genus each. Some genera are much more speciose than others, with the genus Halophila having the most seagrass species. There are roughly the same number of temperate and tropical seagrass genera as well as species. The most widely distributed seagrass is Ruppia maritima, which occurs in tropical and temperate zones in a wide variety of habitats. Seagrass bioregions at the scale of ocean basins are identified based on species distributions which are supported by genetic patterns of diversity. Seagrass bioregions provide a useful framework for interpreting ecological, physiological and genetic results collected in specific locations or from particular species. © 2007 Elsevier B.V. All rights reserved.
From Bonaire, we here provide the first documented case of the green turtle feeding on the invasive seagrass, Halophila stipulacea, in the Caribbean. The seagrass is rapidly invading existing seagrass meadows and altering key foraging habitat of this endangered marine reptile throughout the eastern Caribbean. We expect that more records of green turtles feeding on this invasive species will gradually follow from throughout the region and that the green turtle might alter its foraging behavior in response to the changing species composition of its foraging habitat.
Recent studies show that late stage pelagic larval fish are not simply drifting with the currents as formerly believed, but are in some cases strong swimmers and more than capable of swimming against the ambient flow. There is evidence that larval fish may select specific habitats in which to settle. Although little is understood about their sensory abilities, both sound and smell have been linked to settlement of coral reef larvae (Leis 1997). On Bonaire, Netherlands Antilles, coral reefs, mangrove forests, and seagrass beds provide refuge and food for young fish. Some fish species are thought to spend the juvenile life stages in mangroves and seagrasses and abundances of certain adult reef fish species have been shown to be greater in coral reefs with surrounding seagrasses and mangroves (Mumby 2004). Larval fish may be able to select environments for settlement based on biological attractions detected by certain senses (Lecchini 2005). This study investigates the potential differences in the larval fish recruiting to mangrove and seagrass habitats with larval fish recruiting to coral reef habitats. Samples of larval fish were taken on the three nights surrounding the November new moon. Light traps and dip nets were used at two different sites, one a mangrove/seagrass habitat, and the other a coral reef habitat. Larger numbers of larval fish and more families were represented in the samples taken in the coral reef habitat than the mangrove/seagrass habitat.
Seagrass beds are important habitats associated with coral reefs. Seagrasses are nursery areas for juvenile fish, and they act as buffering zones by dissipating wave energy (Kemp, 2000). In the proposed study, human related impacts on seagrass beds were studied. Many issues affect seagrass beds health, such as water quality decline due to pollution, water temperature rise due to global warming, dragging of fishing nets, dredging, and human recreational activities (Kemp, 2000). This study aimed to measure the potential effects of human recreational activities on the seagrass beds in Sorobon on Lac Bay, Bonaire, an island of the Netherlands Antilles. In the first part of the study, the activities of windsurfers, swimmers, waders, kayakers, and others were monitored, and quantified. The intent was to determine which of these recreational activities may result in damage to seagrass beds in the study area. The second part of the study compared seagrass beds in areas exposed to high human activity to areas where human activities are less frequent, with the intent to assess the relation of health of the beds with high and low levels of human activities. The results of this study show that there is a relationship between human recreational activities and the health of seagrass beds. In areas of high human disturbances, both seagrass percent cover and number of leaves are lower than in areas of low human disturbance. This study also shows that not all human interactions interact with the seagrass habitat in the same amount; different recreational activities interact with the seagrasses in different amounts.
This student research was retrieved from Physis: Journal of Marine Science III (Spring 2008)19: 37-41 from CIEE Bonaire.
The importance of mangrove and seagrass lagoonal habitats as nursery areas for many reef-associated fish species is well established in the scientific literature. However, few studies have examined the relative use by nursery species of different sub-habitats within such systems. Here, we investigated fish community structure of a variety of interconnected sub-habitats of the tropical lagoon of Lac Bay in Bonaire, Dutch Caribbean. Visual census was used to test the degree to which these sub-habitats may differ in their use by fishes of different species and life stages. We quantitatively sampled the fish species abundance, composition, and size structures at a total of 162 sites distributed among nine different sub-habitats that are common to mangrove and seagrass ecosystems. Fish community variables differed consistently among sub-habitats and were mainly influenced by the presence of mangrove root structure or seagrass cover. Mangrove fringe sub-habitats were a premier habitat since multiple life stages of a variety of species showed highest densities and biomass there. Several reef fish species had a distribution pattern suggesting a unique stepwise post-settlement life cycle migration in which larger juveniles and/or subadults appear to move from the open bay environment (seagrass beds or bay mangrove fringe) to the interior mangrove fringes along mangrove pools before later departing to the adult habitat of the coral reef. In the case of the well-lit and well-circulated central bay sub-habitat, the limiting factor to fish abundance and diversity appeared to be the paucity of three-dimensional shelter due to the lack of Thalassia seagrass beds. In the warm and hypersaline backwaters, physiological tolerance limits were likely a key limiting factor. Long-term changes driven by mangrove expansion into this non-estuarine lagoon have been steadily reducing the net coverage of clear bay waters, while the surface of shallow, muddy, and hypersaline backwaters, unusable by key nursery reef fish species, has been increasing by an almost equal amount. Our study shows how fish density varies along the full gradient of sub-habitats found across a tropical bay to provide insight into the potential consequences for nursery habitat function when the availability and quality of these sub-habitats change in response to the long-term dynamic processes of mangrove land reclamation and climate change.
- Protect the seagrass beds at the shoreline of the Blue Zone
- Increase windsurfer compliance to the White Zone no-go boundary
- Reduce recreational user damage to the coral reef
- Floating lines and small floats were installed to protect the seagrass beds in the heavily-used areas at the Sorobon peninsula.
- Turnaround buoys were intended to be placed at the White Zone boundary. As the name implies, windsurfers must turn around at these markers. Commercial use is prohibited in the White Zone.
- Six buoys were placed in the Yellow Zone beside the coral reef. Users are instructed to use caution in this area and reminded that the reef is a “no touch” zone. The buoys are also designated moorings for kayaks.
- An information and awareness program informed users about the issue, the project and the related regulations.
RECOMMENDATIONS FOR MANAGEMENT AND GOVERNMENT POLICY
- Install turnaround buoys to mark the border of the White and Blue zones.
- Contribute funding for ongoing expenses of this project (see 2010 Budget page 5).
- Take measures to reduce the impact of users:
- Correct the footprints of the existing businesses which have encroached beyond their permitted limits.
- Place capacity limits on number of beach chairs, restaurant seating, and number of sailboards rented per day.
- Restrict foot traffic to designated paths to reduce damage to dune vegetation. o Make funds and personnel available to enforce user regulations, most critically during the cruise ship season.
- Do not grant additional business permits for this area until maximum capacity limits have been determined.
- Take measures to reduce vehicle impact to Sorobon peninsula:
- Create a designated parking lot and restrict all public/taxi/tour parking to that lot. Designate narrow driving lanes to reduce the number of cars, compaction of the soil and damage to vegetation.
- Enact policy, regulation and enforcement, and devote adequate funds to manage Lac for the long term.
- Fund and implement the Lac Bay Management Plan (Renken 2003). At the same time, undertake a careful revision of the plan to encompass current conditions and scientific knowledge.
- As part of the above:
- Adopt all recommended Ramsar guidelines.
- Establish and enforce caps on day use-entry to the area.
- Establish and levy a reasonable use fee for businesses (excluding traditional fishing) that use Lac. Dedicate proceeds exclusively for the protection and management of the area.
In 1999 a survey was carried out (Lott, 2000) to estimate the conch population and determine the status of the seagrass beds in Lac Bay, Bonaire. Since 1999 the recreational use of Lac has increased, new structures have been built around Lac and illegal conch fishing still goes on (conch fishing is forbidden by Marine Ordinance of 1991). In order to assess the effects of the moratorium and the impact of increased activity in and around Lac the 1999 survey has been repeated, applying the same methods. Fieldwork was carried out from the end of May 2007 through the beginning of October 2007.
The main conclusion from this study is that the moratorium on conch fishing seems to be effective as Lac Bay’s conch population has increased; however, the cover of turtlegrass has diminished, which is most likely linked to an increase in anthropogenic disturbance of Lac.
- The conch population has increased: in the 51,000 m2 survey area, 223 live conch were found, against 111 in 1999.
- Adult conch were found (4% of the population) while in 1999 no adult conch were recorded.
- The cover of turtlegrass has diminished in most of the 17 grids (2,142 quadrats of 1 m2 ) studied; these grids were spread over Lac Bay. Grid Cai showed no reduction in cover.
- Trampling from windsurfers, snorkelers and other users of Lac Bay plays a major role in the reduction of turtlegrass.
- Cover by macro algae has changed but not necessarily diminished; in some grids the cover increased, in others it decreased.
- The number of most invertebrates has decreased.
- Further study on Lac Bay’s species composition.
- Further study on Lac Bay’s water quality.
This cheat sheet contains photographs of the most common green algae (incl. seagrasses) and brown algae occurring in the Caribbean.