Seagrass Monitoring in Tampa Bay

Program Overview

The Tampa Bay Estuary Program is a partnership of local, state, and federal governments working to achieve the scientifically sound, community-based goals of the Comprehensive Conservation and Management Plan for Tampa Bay (2023 Update). Seagrass was chosen as an indicator of bay health to gauge the success of efforts to improve the bay's water quality. The Habitat Master Plan (2020 Update) established a new goal of at least 40,000 acres of seagrass observed in Tampa Bay (an increase over the previous goal of 38,000 acres). Progress achieving seagrass goals for Tampa Bay is assessed in two ways:

  1. The Tampa Bay Interagency Seagrass Monitoring Program (TBISP) conducts annual on-the-ground assessments along a straight line, or transect, at various fixed locations throughout the bay. These data provide consistent, place-based information to track changes in species abundance and frequency occurrence over time.
  2. The Southwest Florida Water Management District (SWFWMD) collects and interprets aerial photography for seagrass coverage estimates on a biennial basis. These data provide accurate and location-explicit estimates of seagrass coverage to track progress in achieving acreage goals, baywide and by major bay segments.
In-water Seagrass Monitoring Training

Transects

Currently, 61 transects are monitored by local agencies participating in the TBISP. Data is entered using an online form and database. Findings of the Tampa Bay transect program are summarized in technical publications (See Avery and Johansson 2001; 2003; 2005; 2006; 2008; and 2010; Johannsson 2016; and Sherwood et al. 2017) and shown in an interactive dashboard. Assessments conducted during the transect surveys include: (1) measurement of seagrass canopy height, evaluation of seagrass condition, short shoot densities (SSD) and percent coverage for all seagrass species present; (2) characterization of epiphytes observed on seagrass blades; (3) measurement of water depth where seagrass is present; (4) sediment type; and (5) density of all macroalgae species present. Transect data, associated metadata, and a description of how to reproduce TBEP analyses and graphics are also available online.

Seagrass Monitoring

A hands-on field training class is conducted with participating partners in summer prior to the start of the annual transect survey period. The training aims to review sampling procedures and calibrate surveyors by having all partners assess the same training transect. Instructional videos and additional instructional and background materials for the transect monitoring are also available online.

Shortly after the training, comparisons of team surveys are made available on this dashboard. The dashboard provides a simple summary of precision between sampling teams and, if necessary, supports additional training needs to ensure consistency in data collection.

Trends

During more than twenty years of seagrass transect monitoring, the frequency of occurrence (or the percentage of times that a species appears along a transect during a given year) for both Halodule wrightii (Shoal grass) and Syringodium filiforme (Manatee grass) in Tampa Bay has increased (Johansson 2016, Sherwood et al. 2017), while the frequency of occurrence for locations where no seagrass was observed has decreased.

A summary graphic for Frequency of Occurrence over time (how often seagrass shows up at a transect during a given year). Values range from 0% (no seagrass, lighter colors) to 100% (complete coverage, darker more blue colors). Numbers in the cells show the actual percent value.

Bay segment changes over time in frequency of occurrence (how often seagrass shows up at a transect during a given year)

Aerial Analysis

Historical seagrass coverage estimates (ca. 1950 and 1982) for Tampa Bay were obtained through photo-interpretation of aerial images (TBRPC 1986; Haddad 1989; Tomasko et al. 2005). In 1988, the SWFWMD began a biennial seagrass mapping program to assess seagrass coverage and monitor seagrass recovery in Tampa Bay. Prior to 2002, aerial photographs were digitized before mapping (Tomasko et al. 2005). More recent assessments (2004–2020) use digitally acquired aerial imagery. Seagrass coverage estimates are based on images acquired during the late fall or early winter and are classified into two categories: patchy or continuous seagrass coverage (Sherwood et al. 2017). SWFWMD seagrass data in GIS format as well as analysis within a shiny application are available online.

SWFWMD has an interactive story map showing seagrass changes between 1988 and 2014.

Trends

Numerous public and private sector partners have made significant investments to improve water quality in Tampa Bay. As a result, seagrass coverage has generally increased since the 1980s. Coverage estimates from 2014, 2016, and 2018 included more than 40,000 acres of seagrass, a goal identified in the Habitat Master Plan (2020 Update). However, between 2016 and 2022, seagrasses throughout Tampa Bay declined by 28%, or 11,518 acres, to an estimated 30,137 acres (data provided by SWFWMD). The majority of those losses occurred in Old Tampa Bay, which is now at a historic low for seagrass coverage. TBEP and its partners are committed to investigating and addressing the complex causes of observed declines in seagrass resources in Tampa Bay.

Even with losses observed between 2016 and 2022 (SWFWMD data), seagrasses have significantly recovered relative to the 1980s due to improvements in water quality in Tampa Bay.
In 2016, seagrass coverage exceeded levels recorded prior to widespread urbanization within the Tampa Bay watershed. Many locations within the bay proper that contained seagrass in the 1950s also had observable coverage in 2016. The exceptions are primarily in bay segments where historic dredge and fill activities occurred.

Seagrass Species

Five species of seagrass regularly occur in Tampa Bay:

Shoal grass, Halodule wrightii

Shoal grass (Halodule wrightii) is the most common species in the Tampa Bay region. It has narrow, thin, and flat leaves that can grow to about 30 cm (or 1 foot). The leaves grow from short shoots, or seagrass stems, attached to the rhizome, or underground stem. Intact leaves have notched tips similar to a king's crown. This helps differentiate shoal grass and widgeon grass.

Turtle grass, Thalassia testudinum

Turtle grass (Thalassia testudinum) is dominant in more salty areas like Lower Tampa Bay, but can also be found in Old Tampa Bay and Middle Tampa Bay. It has flat, wide, ribbon-like leaves, and can grow to a length of more than 50 cm (nearly 2 feet). Turtle grass produces quarter-sized flowers which are often observed in April-May.

Manatee grass, Syringodium filiforme

Manatee grass (Syringodium filiforme) is found in all subregions except Hillsborough Bay. It has cylindrical leaves that can grow over 60 centimeters in length (about 2 feet).

Widgeon grass, Ruppia Maritima

Widgeon grass (Ruppia maritima) is less abundant in Tampa Bay and occurs in more freshwater areas. Widgeon grass looks similar to Halodule, except that the leaves are alternate, and grow from branching points along the main stem. When flowering, very long and leggy branching is present. Pointed tips on the leaves also help to distinguish this species from Halodule.
Photo source: iNaturalist/jiayizhou-zoe

Star grass, Halophila engelmanii

Star grass (Halophila engelmannii) is also rarely seen in Tampa Bay but is fairly easy to identify. As the name suggests, a group of up to eight short leaves grow from a central base. The leaves are generally less than 3 cm (about 1 inch) long.

Caulerpa sp., Old Tampa Bay

There are also several types of attached and drift algae (large algae that can be seen with the naked eye) that regularly occur in the seagrass beds, such as Caulerpa, a highly variable attached algae, and Ulva, or sea lettuce.
Photo by Joe Whalen

Some people use pasta to help differentiate a few of the seagrass species common in Tampa Bay: Shoal grass is fine like angel hair, Manatee grass is round like bucatini or spaghetti, and Turtle grass is wide and flat like fettuccine or pappardelle. Additional information on these seagrass species and other marine flora commonly found in Tampa Bay is also available.

Other Seagrass Monitoring Programs

Multiple organizations are involved with seagrass monitoring in central Florida and the Gulf of Mexico:

References

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